Is JustEnergy free weekends legitimate?

I talked with a representative from JustEnergy today. She told me about their free weekends plan and showed me the billing statement of a few different customers (I didn't see any personal information, just the numbers). Apparently it's not just free weekends, but they actually credit you back the cost of the power you use on the weekends. One of the examples had an overall rate of 6.5c/kwh. She even recommended that I try to use as much power as I can on the weekend to run up the credit amount and told me a few suggestions on how to do so, like running the AC hard all weekend to get the credit higher.

This seems like there's a billing error in their system, rather than something that the company intended. I'm concerned that they might fix the error and try to claw back money from me eventually. I was even a bit confused about the plan when she first started describing it to me until I looked over the billing statements, because free weekends should be 0 c/kwh, but the billing statements showed -c/kwh.

I signed a contract to switch, but I can cancel for free within 3 business days. Is anyone else on this plan or has heard of anything like this?

In case my description confused anyone, I'll write out a fake example bill from what I saw.

Weekdays 750kwh @20c/kwh $150

Weekends 500kwh @-20c/kwh -$100

Total 1250kwh $50

What it should be for free weekend energy is that weekends are 0 instead of -20, so you get billed $150, not $50.

The contact doesn't say anything about negative c/kwh, only that you get a credit for the energy you use on the weekends. 'credit' is an odd word to use, because it could mean either that weekends are 0, or that weekends are -c/kwh.