I use smbc all the time and it’s fine out for several days (I’m in the UK though so obviously I’d you’re in a warmer climate this wouldn’t hold true for that length of time).
Normal butter can be left out of the fridge for up to 10 days, so add in a ton of sugar and a few days is fine. I should add I do not leave my smbc out for 10 days (although my personal use butter does stay out for many days), just illustrating a point.
The only time I’ve put mine in the fridge was when we were having a heat wave this summer, then I gave it 2hours to come back to room temp before serving (due to the heat this was plenty of time).
Imbc is I believe a bit more stable, but I’ve not made it for a long time so can’t compare. If you ever watch Anne Reardon (how to cook that) she has a YouTube video comparing several types of bc, including how they hold up under heat. It might be useful to you :)
