Well, depending on the quality you might not even feel it off one hit. lol
But generally, a meth high lasts about 8-12 hours (for me at least) It depends on the person...
but that's only if you don't continue to use after the first sesh ;P
Which is unlikely in most cases... heh
It will definitely keep you awake all night.
but people can stay awake smoking for days. I've been there, not my cup of tea, lol.
~Ms.P