We bought through help to buy in 2019.. we never would have been able to buy without it because of the house prices round here. Happy to answer any questions you have
Timescales, it took us just over 5 weeks from reservation to exchange (expected within 28 days by our developer, our mortgage advisor handled it all for us, but our authority to proceed came through really quickly, and then the delay with exchanging was down to our solicitor, the authority to exchange came through quickly too.
One thing (not related to HTB) make sure you do any negotiations for things to be included (upgrades, flooring etc) BEFORE you reserve... we made a big mistake with that