I like to dose it in the morning, it's slightly better absorbed on an empty stomach but it really doesn't matter. Basic info on cialis usually says 'take 1-4 hours before activity' assuming one was taking it for sexual purposes, so I assume it takes some time to take effect. For myself I've noticed it's 'effects' within about 1-2 hours. I work out fasted first thing in the morning so I generally try and take it the last time I get up to piss during the night (I'm drinking lots of water right now), or very first thing rolling out of bed. But in general no I don't think it matters when you take it. Effects from a single dose seem to last about 2 days so I'd probably be just as well taking it at night, but I'm currently low dosing every day and doing some cycling here and there for my own reasons.