if you have not finished the game do not read any further 
IMHO the gman did not "stop' time...exactly...
remember the week long teleport with gordon and alex and teh corresponding conversationa bout it with kleiner? i think what happened was along those lines, the only diffrence was gordon was concious, so to him it would SEEM that "time had stopped" or had slowed VERY much.
truth may be absolute, but time (or rather the perception of time) is relative, and with that thought in mind it may be that what gordon was seeing as the gman doing a bit of grooming on alyx's arm was in fact the gman making her the same offer gordon got in hl1, concluding that bit of business and then getting back to gordon.
in the game we see gordons perception of things, alyx says "we gotta get out of here! maybe we still have..." then enter the gman and his monologue to gordon..fade to black.
alyx's perception could be... her saying "we gotta get out of here! maybe we still have..." just as she turns her head she sees what to her to it looks like time has "stopped". gordon disappears(or most likely he looks frozen just like she did to him if her head turns far enough) and the gman introduces himself and makes his pitch.
from the gmans perspective, he goes and gets freeman, leaves him in "stasis" or wherever he keeps gordon while he "sleeps" for a bit and gets alyx. then finishes up with gordon.
IMHO the gman did not "stop' time...exactly...
remember the week long teleport with gordon and alex and teh corresponding conversationa bout it with kleiner? i think what happened was along those lines, the only diffrence was gordon was concious, so to him it would SEEM that "time had stopped" or had slowed VERY much.
truth may be absolute, but time (or rather the perception of time) is relative, and with that thought in mind it may be that what gordon was seeing as the gman doing a bit of grooming on alyx's arm was in fact the gman making her the same offer gordon got in hl1, concluding that bit of business and then getting back to gordon.
in the game we see gordons perception of things, alyx says "we gotta get out of here! maybe we still have..." then enter the gman and his monologue to gordon..fade to black.
alyx's perception could be... her saying "we gotta get out of here! maybe we still have..." just as she turns her head she sees what to her to it looks like time has "stopped". gordon disappears(or most likely he looks frozen just like she did to him if her head turns far enough) and the gman introduces himself and makes his pitch.
from the gmans perspective, he goes and gets freeman, leaves him in "stasis" or wherever he keeps gordon while he "sleeps" for a bit and gets alyx. then finishes up with gordon.
