At a minimum, service all belts based on manufacturer's recommendations listed in the vehicle's owner's manual.
Different makes and models of cars have vastly different service intervals when it comes to timing belt replacement fwiw. A family member of mine has a Daewoo Lanos that requires a timing belt change every 60Kmi. according to the owner's manual and I've had other cars that don't require a change until 120K mi.
As for the other squeaking sound, I'd guess your serpentine belt is due to be replaced very soon regardless of the recommended service interval. Often when you hear a squealing sound for 20-30 seconds right after startup it signals a serpentine belt on its last legs.