There isn’t a number of hours prescribed for a 1st solo, I just remember you that the conditions are:
1. The students is ready and feels himself good
2. The instructor feels himself good too!
3. The weather is OK
4. the plane is OK
Between a solo at 10 hours and another at 20, there are only 10 hours of flight. For a pilot career what can represent 10 hours of flight? On the contrary an accident at the 1st solo could mark or stop forever a student pilot training.
Be confident!