Well I wished I had been given a penny for every groundspeed check I did using DME when I was on the B737-200!!
For a quick check 36 secs is OK but I used to used 3 or even 6 mins if I wanted a really accurate one.
Mind you, after a while you got that good at it that you could watch the DME (barrel type presentation) rate of change and take a good guess at the groundspeed.
It was quite amusing after a long day to be airtaxied back home and they had groundspeed and time to station read out - such luxuries!!