The "you should renew your registration" (or equivalent) are starting 30 days before the end of the previous validity. I agree that 30 days seems "too early", but there is something more important than that.
A user register for a year, not 11 months. There should be a way to "temporarily pause" this type of notifications. If I start to receive them today, I should be able to, either:
A) renew immediately (already available); or,
B) show the notification next time (already available if nothing is done); or,
C) skip the next notifications for "X" days, so for "X" days avast should not keep bothering me with the same remainder; or
D) the next notification should appear only the day before the expiration day (or even the same day).
The user would be notified, and not be bothered with the same notification every 4 hours (currently, 30 x 6 x 4 = 720 remainders), unless he wants to be reminded every 4 hours.
The "X" days could be, for example:
_ 14 days when "30 to 23" days for expiration arrives;
_ 7 days when "22 to 10" days for expiration arrives;
_ once a day when less than 10 days;
_ every update attempt for the last day;
_ the user should choose either to keep receiving the remainders after the registration is expired or not at all.
This is just an example, and the implementation could be different in several aspects.
All this is specially important to paying users (but could include avast free anyway), that keep complaining after 11 months.
This could be implemented for Avast 7.