I'm not really sure if anything has changed since ye olde 75 cap, but here's some general Charm duration info
and what you can roughly expect
in terms of duration in Adoulin areas.
I can't quite recall what the duration of EM~T pets was like back at 75-cap... But 3~5ish mins sounds about right (used to use Demonic Pugil vs Doom Guard/Warlock for merits back then, haha). With lots of Charm+ gear now, you can hold Decent Challenge pets for like 15 minutes+... And the Tough monsters last long enough for most fights, so it works out well. Not much need to swap.
There are some Tough ladybugs on the West end of Ceizak Battlegrounds if you want some free TH1, hah. :)