Traditionally, at a "closing" between solicitors, they met in person at a nominated time and title deeds and keys were exchanged for purchase money.
However, nowadays (certainly in the last 4-5 years or so) it's far more common that there's no meeting, and closings are done by post/courier. So the time of the actual closing varies considerably.
For that reason, in the case of new builds, keys are handed over on site, and for second hand, the buyer collects them from the estate agent. Your solicitor will then make arrangements to meet you to sign the final transfer deed at a time convenient to all of you.
If you want, call the estate agent in advance to make sure they have a set of keys.
Good luck!