I've recently activated the "On-Demand Renewals" option, leaving the default values, so 366 days for annual renewal.
It's all fine, except for the notification in the client area.
If the service is due in 9 months, for example, the client sees a notification stating "You have 1 service(s) that are due for renewal soon."
I find it bothering for the client: 9 months is NOT soon, and there is no way to give the client the possibility to renew soon without pressing him/her with that incorrect notification.
Giving the possibility to renew on demand only means that the service CAN be renewed, not that is due for renewal. I would consider it as "due" maybe after the invoice is generated only.