I see the purpose of the timer as a safety cutoff, in the rare event that the charger fails to shutoff. With most batteries, the BMS is what stops charging by refusing to accept any more current. As a result the charger light turns green. It requires a BMS failure then for the charging to continue, If the BMS has failed in this respect, it may let you down on its other protective duties.
I used to use a timer, but with sevral batteries and several ebikes, it got unwieldy. Now I just try to remember to unplug everything before I retire for the night,