I'd say you've got 2-3 weeks minimum. Also consider the type of high your looking for. Harvest sooner for a more uplifting cerebral kind of high. Wait a little longer the the full body couch lock kind of high.
90 cm high minus 13 cm for the lamp and them another 20 cm for the distance you'll need to keep the light away from the tops of you plants. You're left with only 57 cm for your plants and that doesn't include the size of the pot.
The stoner doth protest too much, methinks. Getting anger and acting insulated only made you look guilty. Had you requested a manager, he/she would have thought the exact same thing.
You could have said: We volunteer at our church. We're going to be planting flowers with a group of kids for...