Single-turn equipment changes don't take any time. The turn count will advance by 1, but no in-game time will pass, and monsters don't get a chance to act.
Fixed. But any such fear strikes into my heart as the whole energy/speed/event queue thing in ADOM is probably the most complicated part of the whole game (and there are many truly complicated parts) and it is so easy to break something non-obvious. During my limited tests everything looked fine but these problems (and their solutions) strike a dark and grim fear into my heart...