There's two cases here, charging "in-use" cells & maintaining cells in "storage" & these scenarios are different.
In-use I'd fully charge, use, recharge, etc (see below re <0C temps).
For storage I'd use the cells down to approx 60-70% & leave there, charge a little if needed, they should hold charge for months no problem unless there's drain, eg the BMS or use, etc. Storage at full charge (ie over approx 80-90% SoC) is not considered ideal.
I'd also consider the temperature curve of the cells you have, ideal voltages may change if cells cold vs warm, etc.
Personally I don't like my cells going over about 3.40V at full charge at the typically about 15 to 30C temps here.
Regularly taking LiFePo4 cells to >3.50 damages them & doesn't give you more SoC, there's very little % above 3.40V
Balance in my packs becomes unstable if cells >3.40V, some cells start to rise fast.
In winter if the cells are below freezing you need to be very careful not to charge Li cells much or at all.
If they are above 0C charge gently & above about 5C normal charging should be OK but check the manufacturers spec for your cells.