Depends on the builder. Some take the HTB as part of the 10% some don’t.
It should be stated in the contract, it was for mine.
I paid 7 booking deposit, 17.9 HTB and paid the balance of 10.9 when when signing the contract. I’ve another 10% waiting to pay off at closing which I’ve held onto.
They’ll require you to complete step two of the HTB on revenue to get the claim code and send them to the solicitor before they can claim the HTB rebate. You can only get these once you’ve uploaded your contract and your bank loan offer letter.