time dissociation when clean

Hello! I'm not new to smoking weed, although lately I have been smoking (well, with a bong) around twice/thrice a day. I don't plan to get real high, so it's just the right amount to feel something and still be able to go on with my daily life (studying, etc..). Thing is, I kinda lost sense of time, as in, i may be sitting for which i think were 5 minutes and 20 have passed and I don't really recall doing much in that period of time, and it happens when i'm not high or even if I haven't smoked anything. SO... is this normal? is it just adjustment ? Thank you so much.