It is five days. It is probably due to how many there are and they are only temporary because they are part of the promo.

Blue Menelaus:
Objective: Take part in competitions - 0.1 points per competition participation

Have to say I really hope this is based on the amount of horses you own. I own VIP so it will not be a problem. But it will be a nightmare for those that don't have auto comp and have a ton of horses.

How to play?

To get a Wandering Horse, collect points by:
performing the requested action as many times as needed or
by giving them the right color pollen (except for the horseAtlas).
When you get 100 points, the horse joins you in-game for 5 days with their present or presents!

You can get pollen:
*in UFOs
*by buying them with passes
Jackpot
Win the divine horse Ptah at the same time as Wandering HorseAtlas.


Ptah is one of the Egyptian horses.
He will offer you one treasure when he wakes up each day.
By scratching the treasure chest, you have a chance to win:
1 x Bonus Pack
Iron
Skill points you can assign as desired to any of Ptah's skills
This horse cannot be sold.

See a list of everyone who owns Ptah
Golden horseshoes:

You can also earn golden horseshoes for the Event trophy once you've collected:
1 Wandering Horse
6 Wandering Horses
11 Wandering Horses
16 Wandering Horses

Dynamine

(Forgot to get picture of chrysalis...)

Glasswing




Blue Menelaus




Swallowtail



Leopard Scribonia


Atlas


Not yet unlocked:

Ptah is one of the Egyptian horses.
He will offer you one treasure when he wakes up each day.
By scratching the treasure chest, you have a chance to win:
1 x Bonus Pack
Iron
Skill points you can assign as desired to any of Ptah's skills
This horse cannot be sold.

1 x Philotes' Stroke
1 x Medusa's Blood
1 x 100 x Carrot
1 x 5,000 Equus
1 x 1 x Fertility Wand
1 x Achilles' Heel
1 x Hera's Pack
Use within 90 days.
1 x Shower
1 x Themis' Scale
1 x Bonus Pack
1 x Horseshoe Studs
1 x The 5th Element
50 x Flax
1 x Pink 2** polo wraps
1 x Croesus' Fortune
100 x Leather
1 x Black and pink 2** Classical saddle cloth
20 x Aging point
1 x Tractor
1 x 3*** Classical Saddle
1 x Spurs
1 x Ploutos' Parchment
1 x Horn of Plenty
Use within 90 days.
1 x Black and pink 2** ear bonnet
1 x 3*** Classical Bridle
1 x Apollo's Lyre
1 x Zeus' Lightning Bolt
1 x Harmony Pack
Use within 90 days.
1 x Water of Youth
1 x Nyx Pack
Use within 90 days.
1 x Bell boots
1 x Black Orchid

Dynamine

100 carrot, 1,000 equus, 1 x Fertility Wand

Swallowtail

10,000 equus, 1 x Bonus Pack

Glasswing

1 x Philotes' Stroke, 1 x Medusa's Blood

Blue Menelaus

1 x Achilles' Heel, 1 x Hera's Pack (Use within 90 days)

Leopard Scribonia

1 x Shower, 1 x Themis' Scale

Begin lyrael's post.
(Monarch
- Zeus' Lighting Bolt and timed Harmony Pack

Blue Icarus
- Tractor and 50,000 equus

Tailed Jay
- 20 APs and timed Horn of Plenty

Orange Tip
- 3*** Classical Saddle, Spurs and P.Parchment

Death's Head
- 100 x leather, 2** saddle cloth, 10 APs

Swallowtail
- 10,000 equus and Bonus Pack

Red Admiral
- 2** bonnet, 3*** briddle, Apollo's Lyre

Poplar Admiral
- 50x flax, 2** polo wraps, Croesus' Fortune

Daggerwing
- Bellboots, 5,000 equus and Black Orchid

Brimstone
- Water of Youth and timed Nyx Pack

Spanish Moon
- Horseshoe Studs, 5th Element

Timed items have limit of 90 days)
End lyrael's post.

Atlas


1 x Ptah

Swallowtail:
Objective : Stroke a horse in the Safe Haven - 6 points per horse stroked

Glasswing:
Objective: Log in for the first time of the day - 6 points per first login of the day

Blue Menelaus:
Objective: Take part in competitions - 0.1 points per competition participation

Leopard Scribonia:
Objective: Donate pollen to other Wandering Horses - 0.3 points per bit of pollen donated

Monarch
- Remove Pegasus or Winged Uni wings

Blue Icarus
- Donate horses to Ow

Tailed Jay
- Give birth to unicorns

Orange Tip
- Gift shop items to friends


Death's Head
- Give apples to other players' horses


Swallowtail
- Stroke horses in Safe Haven


Red Admiral
- Take horses for rides


Poplar Admiral
- Do foal games

Daggerwing
- Give mashes to horses


Brimstone
- Open Horns of Plenty


Spanish Moon
- Age horses to xx years (Live version's aging date is unknown.)

Atlas:
Objective: Get the other Wandering Horses - 7 points per Wandering Horse obtained

After a very long time, the Wandering Horses are finally back!

Collect all 16 Butterfly Wandering Horses and win prizes!

There are 16 Wandering Horses, each representing a species of butterfly. Each Wandering Horse has a meter that can be filled by completing an objective or by a pollen donation of a certain color, depending on the horse.

The objectives can be repeated as many times as needed.

When the meter reaches 100 points, you get the Wandering Horse in your breeding farm for five days, as well as the prizes linked to it.

Warning: The birthday objective ("celebrate a horse's 30th birthday") will be higher on the live game.

Major differences compared to previous Wandering Horses contests

You no longer get points for the Wandering horses in the Horn of Plenty as previously. Now you have to use pollen (which can be purchased directly during special offers with pollen packs)

You can’t get all Wandering horses from the first day. You can unlock 3 on the first day (during the tutorial) + the Wandering horse giving the divine. The following horses will become available at a 2/day rate.

Before you unlock them, you can’t start collecting points for them.

Wandering horse promotion. I'm going to get as many as I possibly can without spending too many passes.

To everyone else out there who needs to prepare, save up a bunch of horses who can do foal games, rides, and competitions, and save up a bunch of horses that are close to 30, too!

Monarch.

The Alchemist packs will appear in the black market. When I click through now it doesn't give me an option to buy.

For the raising a horse to x years objective, it could be 40 and not 30 when it reaches the live server. So look out for horses in the sales with M.Arms and/or work on your AP stash(5 years=30 APs). Also stock up on Black Orchids in case you need to keep older mortal horses alive. The objective could specifically be mortal horses only.

A way to kill a few birds with one stone.

Buy older mortal pegs, age them up to near 30 over the next few weeks. When the promo starts you can dewing for one WH, then continue to age to 30/40 for another. Then send them off to heaven to get passes for the HoP objective.

Or keep the pass horses you already have for September, don't send them off in the first few days but wait until the promo starts.

For things like giving apples to other players horses. If you do xanthos/topaz/frost each day. Give them an apple while you're already on their page.

Keep your gifting to friends slots free on the week the promo is to start.

If this is the same as previous WH promos, everything will be laid out in advance. So you can decide whether to go for specific gifts or aim for the divine.

Giving yellow pollen to Scribonia itself is cheaper, so the best method is to use all yellow pollen you have on Scribonia, then other colour pollens on the others, to get extra points for Scribonia. Later there might be a special offer on pollen, so it gets even cheaper.