Handyman has fixed leak from upstairs bathroom (he thinks..). I've put de-humidifier on. If the leak has been fixed how long before it starts to dry out? And before I can paint on ceiling?

this will depend on the size and type of dehumidifier used,make sure that you kep the door to bathroom shut as the dehumidifier will draw from other parts of the house , when the unit stops filling up you should be ok, regards Terry.

How long is a piece of string? Depends on how wet it got........I would leave de-humidifier for at least a week or until it stops collecting water. Remember to treat the ceiling with a damp seal before you re-paint otherwise the brown stains will just keep reappearing I hope this helps