Exsp33db1rd said,
not a criticism, but I agree with NigelOnDraft, in operating 4 eng. heavies from 1958 to 1994, I also never even heard of timing to V1, but that doesn't mean it was never suggested,
we used a minimum acceleration check when I was in the USAF. Don't know if they still do but it was based on reach x velocity by the 1000ft or 2000ft marker. Very useful in the old KC-135 'water wagon'. We also computed a time.
Based on that previous practice, I began timing my takeoffs. I can't remember the exact numbers (now retired) but I think it was something like :30 seconds from application of takeoff thrust to rotation. IF it took more than :30 seconds you were heavy and if it took :45 seconds, you were very heavy.
Also, I seem to remember at least 80kts by 1000ft and about 120-125kt by the 2000ft point. I will have to begin timing my takeoffs again. It is not really relevant for my airplane now (C-II) as we don't operate off anything but long runways.