If your child studies with me, they have likely already received an ear full of chatter regarding practice methods. I hope that they will manage to take their bassoons out every day and spend some time, but I have no hard "rules" regarding how much time they should be spending.
What should they be doing? SLOW, careful, mindful practice to start. YES, we all hate to go slow. But the slower and more exacting one begins (and continues), the less time one must ultimately spend undoing mistakes made by rushing through. The study referenced below explains the theory and the testing of it far better than I could:
Freelance bassoonist and carpenter of the reedy persuasion, residing and thriving in Tucson, AZ.
Habits of Musicians
Have Bassoon Will Cook
The Pedantic Bassoonist
Double Reed Ltd.