This spell sounds like it could be extremely powerful out of combat. The great macguffin is in a heavily trapped and guarded room. Time stop might enable you to ignore traps, bypass guards, grab the macguffin and get out.
It seems like a spell that you wouldn't cast every day, but would learn for particular planned tasks.
They have to be
very well planned tasks which you can complete in 2 rounds, if you want to make sure it works in the worse case. If it takes 3/4/5 rounds, you have 75%/50%/25% chance respectively that such plan would work.
This. It is a terrible combat spell, but one of the most powerful exploration spells in the book.
As such, I don't think I'd often bother to prepare it unless I knew I'd have a reason to cast it. On most days, you will find there are far better uses for your 9th-level spell slot.
Exploration usually requires
carefulness. Ho much can you explore in 30 seconds?
I am not a huge fan of combat spells, but if they wanted to make Time Stop a non-combat spells, then keeping a 1-5 round duration is a mistake.
OTOH, I can totally see that different DMs are going to interpret the spell's limitation differently: some DM can say that "affect" a creature means directly harm and thus allow a Fireball to work (on the ground that it affects an
area and not a creature directly); other DM, probably the majority, will consider indirect harm as ending the spell; other DM can even ban the "steal an item" application, since this could indeed qualify as affecting it; yet other DM can extend the meaning of "affect" to really make it useless in combat if they want so.
I don't know how I'll handle it, if I ever DM the game up to that level, but I do know that from a spell (or anything in the game) I require it to be
usable but not
abusable. There's a range between the two, so it's not that I need to surgically dissect the spell's text to find "the" correct way to use it. But if the rulings make it fall out of this range, then it's just better to remove the spell from the game.