APE time stamp
From Hydrogenaudio Knowledgebase
Time stamps are used to address something inside the encoded audio title. Time is relative to the title start, time distance is normally small (some minutes up to one or two hours), accuracy can be from 1 seconds downto 1 sample.
For sample accurate addressing you need at least 4 digits (fs <= 10 kHz) or 5 digits (fs <= 100 kHz). Written item must be rounded up, recalculating sample then do a rounding down.
Hours and minutes can be encoded using two or one colon before the seconds. But it is also possible only to write seconds. Parts of a second can be added after a period.