Ok thanks you for your help
Personally I would ride for 40 mins to an hour. My instructor says if you ride for any longer than that then the horse will eventually lose energy and won't be able to do what you need it to do.
Depends if you do it everyday once every now and then is not going to kill her and depends how fit she is and how big or how intense your flatwork is. As a child I used to ride twice a day but I did very chilled jumping and flatwork and it was on a weekend every now and then.
It depends on the pony. If she's currently in work, then start with whatever she's used to doing and build up, otherwise start from scratch with half hour walk rides and build from there. Also it's best not to jump them every day, it's really hard on their muscles and joints. Twice a week jumping is usually enough.
I would do a hour a day and giver the horse a break like twice a week
If the pony you are getting isn't fit, you should ease into a regular routine. Also, jumping a horse every day will wear it out very quickly and is extremely straining on their legs.