guidance for using timeout_multiplier?

On my Mac, some tests time out (as "unexpected") during my validation runs. hClose002(ghci) is a reproducible example for me. When I do a --slow run, this ends up taking a lot of time with the default timeout of 300 seconds. Is it sensible for me to add the timeout_multiplier setup function in the respective all.T files if I can reproduce the time out? It looks like 3 seconds ought to be fine for the ones I've investigated so far, so I was thinking of passing 0.01. Thoughts? Thanks.