As long as s/he likes to learn chess and likes to play chess, 1, 2, or 3 hours are all fine. If s/he does not like to play chess, then 0 hour. Of course, the more time s/he puts in, the more s/he could achieve.
There is no genius in this world. All chess kids are smart. If you expect your child spends 10 minutes a day on chess and wins the national, you are dreaming. You can either find excuses for your child (and yourself) or help your child find time. There is no third way.