I do the same. 30 mins, then whenever I finish the beer I'm currently working on I strain and then sparge the grain. I'll confess I haven't experiemented with 60 mins, but all the research I've done seems to suggest that you're not really gaining anything after 40-45 mins.
It doesn't hurt anything to go longer, but since you're not getting anything out of it, it doesn't really make sense to.