Take a peek in the bag and see if the soil itself is dry. If it's still moist, you're good, if not, give it a little watering. I try not to get it soggy, just damp, as it won't be able to evaporate as quickly in the bag. You don't want your leaves to rot. The moisture in the bag will help in keeping the leaves from drying out, but eventually, having no soil moisture will dry them out. I have had mine in a south window as well, they were perfectly fine there. Just a hint, if they get some direct/strong sun (mine is through a sheer but it doesn't diminish it much) you will get a lot of condensation on the bag and the soil dries out faster. I'm not sure how much warmth helps - it probably does - but mine sat in that same window all winter and did fine.

Please be very careful with leaves or plants in a bag, plastic box, deli container, etc. It these containers are placed in a sunny window, solar gain can occur and they can cook in a heartbeat. It's much safer with no sun exposure but bright light.

Barbara