We purchase our house in April, 2018 and filed for homestead exemption. That has not reflected in the tax bill. When will the exemption available?

I believe you have to have been living in your house before January 1st. You will get it for next year, but if you call them they will explain it to you.

Your exemption will begin for the 2019 tax bill. The tax bills reflect the state of the property on January 1st of each tax year, since you were not the owner of record on January 1st, your exemption gets refected on the next tax bill in November of 2019