Start the stopwatch going over the hold fix, and note how long it is before you need to pass over the fix again. Go outbound until the stopwatch says half that time is up, and turn inbound again. You’ll need to make an educated guess at a wind adjustment, but (at least in Oz) you’re allowed to be up to a minute early. Using a time marker and judicious speed adjustments, it should be possible to be within a few seconds.