If it is a photoperiod plant and it is flowering, putting into a tent at 18/6 will cause it to revert back to vegetative growth and cease flowering, so leaving it on the window sill or only giving 12 hours of light and 12 hours of absolute darkness are your only options.
If it is an auto plant, putting it in your tent at 18/6 will have no adverse effect on its flowering cycle.
Hope this helps,......... Organoman.