Oh I run into this situation all the time... listen up

Estimate that your parents will be home by 4.
Go to the garden or any place outdoors. If indoors then just open the window.
Spark up at exactly 12-1.
The average high lasts 3 hours. After 3 hours, you will be sober and if your parents walk in, you will be sober enough to welcome them normally.

I would try to get the weed earlier though.. like at 10am. Especially if it's chronic, you might be really high for 5 hours if its that good. So try to smoke up by 11. That's almost a wake n bake thing. If I were you I'd go munchy shopping on tuesday and clean my whole room and have the most perfect day on wednesday. You sure you can't just get the chronic on Tues?