So it's monday night and my "Weekly Heroic Strike" doesn't reset.
I thought that you can do it whenever in the week and Sunday night it will be reset. Or do I have to wait 1 week and then i can do it again? thx.
The weekly reset for heroic strikes is Tuesdays at 2:00 AM PDT.
The weekly events reset based on UTC time. This means that depending on day light savings your local time may change.
For example, at the time of writing this because day light savings occurred recently, the weekly reset for PDT is Tuesdays at 1:00 AM.
Bungie's help article (linked by Rapitor) clearly states "Event resets happen every Tuesday morning at 9:00 AM UTC."
Although the reset occurs at 9:00 AM UTC, if you are already playing Destiny at the time of the reset, you must log out (for example, by selecting "Change Character") and then log back in in order to see the icons as not filled in and also in order to get the rewards. If you do not relog in this fashion and do the weekly while it is still filled in (and no rewards show in the launch screen) you will have to do it again.
Tuesday 00:01 UTC it's because that's when the game was released