ball pythons are known for goin of feeding, even upto a year is not uncommon especially during winter/breeding season, there were even 2 cases of ball pytons goin off food for 22 months which is almost 2 years now im sure they were adults and not babies, now i stick to a stict feedin schedule:
babies/yearlings - offer food every 5-7 days
1 year olds and up - offer food every 7-10 days

now i say offer food becuase if they dont eat they dont eat and get food offered the next scheduled day, if you have a snake who didnt eat and u keep tryin everyday this will stress him out, another thing is you should weigh your snakes i weigh my snakes before every food offering that way i can see if they are losing weight, if your snake isnt eating and losing weight then you have something to worry about


last thing is i wouldnt suggest leaving a rat/mouse with ur snake unattended . . . you said you leave the mouse in there for 20-30 mins but check every so often, thats a bad idea if you have a live mouse in there you should watch the whole time it only takes about 3 seconds for a mouse to bit a snake . . . prekilled no problem live feeders must be watched at all times

hope this helps!!!