log retention question

I assume that "log.retention.hours" means the number of hours since the log
file was last modified, correct? Or is it since the log file was created?

If I set "log.retention.hours" to 48 hours does that mean that _any_ log
file older than 48 hours will be deleted or only log files that have
reached the maximum size ("log.segment.bytes") and are older than 48 hours
will be deleted?

In other words, will a log file that's actively being written to be deleted
after "log.retention.hours" has passed?