I time the preceding's positive start of rolling. Probably not scientifically exact, but good enough for me in practical terms, to reach its wake in later than two minutes. Most likely my liftoff point comes earlier as well.
The ATC has been always helpful as far as I can remember. Either delaying the take off clearance or amending it with an advisory. I suppose individual ATC's procedures may differ.
"Caution wake turbulence, behind departing XY triple-seven, cleared for take-off Rnn".