I'd say they should leave you alone if you don't appear to be convulsing or anything, but 5 to 20 minutes is on the mark for me.
Not leave you alone literally of course, but try not to talk or make noises that will disturb your trip, unless you feel uncomfortable and ask them to talk to you.
I had my girlfriend sit a few of my trips, then I really just got confident that it would be better by myself, because she can't help but show concern and say "you ok?" when I'm finding something to be overwhelming during the trip, and that messes it up for me.
I find getting up and moving to be very difficult on low doses of dmt, and on a hyperspace dose I'm pretty much completely immobilized, able to only move my arms and hand and roll over, which is why i rationalized doing it in bed by myself.
I'm not saying to go through it without a trip sitter if you can avoid it.
I'm not sure if you've been to hyperspace before but I feel like simply the fact that you are alone can be confusing when you come back and have noone to explain it to.
This is only based on my personal experience, as I don't really have any close friends who do dmt regularly, and I really wouldn't want anyone I haven't developed some sort of serious bond with to go through the experience with me.
All in all I think most of the danger would exist coming back from the trip and freaking out about what happened while you were there, than anything seriously going wrong with the dmt in your system, of course, this is speculation and should be regarded as such.
I love you, and I hope your travels are safe. I wish I could find someone who was as interested in this experience as I am, it would bring alot of comfort.
Death is an awakening. . . One day it will come.
But you'll search the skies with your eyes in frantic wonder.
You will come to realize the lies you've told yourself for so long to survive.
"We fear something that does not exist."
Not only does death not exist, we ourselves do not exist.