When you put the nappies on the clothes horse use pegs. This will dry them faster as they are not folded over. Also top n tail them during the day as this will help dry them.
I used to wash at night and hang them on the clothes horse over night. If it was sunny the next day I would take the clothes horse outside to get fresh air on the nappies. If you have them outside make sure they are in by 3.30 so the night air doesn't make them damp again.