I never warm up most of the time. If you know how to make balls, you know
how, and you aren't going to 'learn' 15 minutes before a match. BUT, if I have
a real tough match for my first match in a tournament, I practice 'bank' shots
to be sure I am tuned up for banking on that table.
If you are an experienced player, and have good stroke mechanics, then the
only reason someone takes a long time to warm up is because their 'mind' is
not right. I have always believed in the 'mind, body, and spirit' thing, and
if your mind is not ready to win, you won't, simple as that.
Rather than just banging balls around or shooting shots on the table that I almost never miss, I sit on the sidelines getting my mind ready for the upcoming matches, and at the same time I rather observe and size up my possible opponents. This way, I am ready mentally to play my best in upcoming matches. Works for me ...