engine:
Does 5th Edition handle time in any different way? The odd thing for me about rituals is that once things aren't listed in rounds or last longer than a short rest and shorter than a few hours, there's no clear way to make the time matter. One could decide that there are wandering monsters every 10 minutes, or something, but I don't remember seeing any rules guidance on that.
I'm puzzled by this statement. The rules state pretty clearly that the ritual takes "ten minutes longer to cast than normal." So, if you're casting Alarm, it would take 11 minutes and not use up a spell slot. Duration would be the same, everything else would be the same. Elegant and straightforward :-)
The rituals in 4e are interesting for the same reason that they're more complex: they are their own distinct thread, something you keep track of and have to learn distinctly. That's also why I've avoided them in a player--the more things I have to keep track of on a character, the worse things are for me. The slayer fighter is my favorite class for a reason. :-)