GTA foroward charge

we are going to start GTA business from 1/4/2020. we decided to Bill our clients foroward basic 12% tax. we will purchase few of truck for our business purpose.
we expect trucks will purchase April 20 but bill to out clients will start from May or June 20.

now questions is can I claim ITC on purchase of truck in April 20 Return? We expect output sell will be nil for the month of April 20 . I want to know can I take ITC even there will no out put tax or before sell bill start