I was taught that the official way to do it is to time from over or abeam the fix. However, it makes it easier to get onto the inbound track if you've got some extra space to do it, so timing from wings level is the way to do it provided you're not going to go anywhere near the edge of the protected area. IIRC the holds are designed for a max of 170 kts for A/B aircraft, so most training aircraft stay well within.