How long does BBT stay elevated?

Marissa • 27 years old, married since July 2, 2013. Beautiful daughter born 02/11/15 ❤ Handsome son 12/09/18 🌈
How long does it usually take bbt to drop to normal again after a positive opk? I got my positive opk on 5/24, and so far my bbt hasn't dropped again yet. Is that normal?