Need to wait 24h after clean same for frying pan
Lechumra alte rebbe
Many people hold this way (lechatchila), in particular chassidim. They won't use a ben yomo meat pot for fish and vice versa. Some even have a separate fish pot.
The OU statement above was probably in line with this shita, lechatchila.
Practically speaking, cleaning off any mamoshus (actual particles) and bringing it to the highest (used) heat for a few minutes would be enough.
(Leaving the MG"A aside, there is a whole other discussion to be had, which is "do we say sakana on bleeos?" The answer to that has a lot to do with the varying psakim in the OP shayla)