I see what you mean, and I'm not saying they should never get towed. OP should have just waited until the spot was needed to tow (or a couple hours before to make sure everything is done in time.)

It would have been ideal if the person using the spot asked OP for permission, but it's possible the spots aren't marked with names or they didn't want to bother someone before 7am.

Just think of it in terms of pros and cons. What does OP gain by towing the car early? Almost nothing, unless there's more to the story that's missing. On the other hand, towing the car early removes the possibility that the person comes back for their car before 7pm and costs that person potentially hundreds of dollars.