Or plait up then take a pair of tights and secure with rubber bands over each plait - also plait up with setting lotion (the stuff old ladies use on their blue rinses) and hairspray them to glue stray hairs down. (Donkeys plaits stay in for at least a week even when I have taken the thread out - they are glued in!!!)
Overnight plaits will rarely look as good as ones done the same day - but if your horse has a good manefor plaiting (i.e. the hair is all the same length) then you may be OK. Use something like Quicbraid when you are plaiting (or setting lotion as SSM says) and that will stop them going too wispy. A hood may work, but if the horse feels itchy, then they will rub them, which means that some of the hair may fall out. If you practice, you will get the plaiting time down to less than 30 minutes, and then can do them on the day which is probably more comfortable for your horse!
Agree that plaites done the night before don't look so good but if your horse is like mine and won't stand still once she has been in over night then I understand they need to be done the night before.
I sometimes just plait them the night before and roll them up and sew them in the next morning. I use lots of firm hold gel and hairspray and if i'm going to roll I use tights and a hood overnight.
I always plait the night before esp if I've got an early start. I think it helps my boys plaits look tidier as he has a few random bits of spikey hair that refuse to be plaited!!
My tips...I use strong hold gel, then plait with bands (hate sewing!!), then a bit more gel to tidy the random bits, then he wears s snuggy hoods turnout hood and looks like a bank robber!! I find the turnout hood heavier and doesn't slide around as much as the thin lycra ones! I'm lucky tho as my horse doesn't tend to rub his plaits
Quicbraid is brill, but honestly over night plaits always look worse than same day plaits.
I never understand people who want to the night before. But have seen a number of tights and odd jay cloths tied over plaits.
Less than 30 minutes...???? Try plaiting 3 hunters in 30 minutes in Jan when you can't even feel your fingers! Seriously though for eventing I almost always plait the night before as almost tidy is tidy enough. For proper showing I would always plait on the day, even if it means getting up at 3.30am instead of 4.00.