what am I supposed to do then ? like 30.5s is not enough to be able to have the game started at that point so I can't do the reset at 0.00, does anyone have a clue on why my 3ds is so slow ?

You could set your time to one minute earlier and go with -1:30.5, I guess...? I know it's not satisfying, but if your 3DS really is that slow then it might be your only solution :/

If that works it might be my only solution so thank you very much I will do that