Payment of enrollment and tuition fee

[Unohu]

Hi,
We are looking at moving into Singapore sometime around July 2019. We have applied in two schools already since our son starts grade 9 next year and seats may be limited.

While our second choice of school has given conditional acceptance, our first choice of school will only let us know by April if there are seats available in that grade.

While we have already paid the application fee for both schools right now, we would obviously not want to pay the rest of the money for the second choice of school and then repent later if we get through the first choice.

Does anyone know when schools generally ask to pay the enrollment / tuition fee for a new joinee. Is it immediately to confirm seat?

Thanks for your help.