Warming up for WHAT?
Just to... warm up for your ride? Or are you warming up for a 60-minute Pro/1/2 crit? How old are you? Is it a morning race and you're a night person? How hard will you be going?
Sorry, but without answers to those questions it's impossible to answer. I'm 41 years old and regularly compete in Masters and Pro/1/2 criteriums; usually between 40 and 90 minutes. The effort in the race is rather intense and starts almost immediately after the whistle. Because of this, my warmup can take up to an hour for me to reach correct operating temperature.
If I do a long road race (which I try to avoid, but end up doing anyway) 20 minutes of easy spinning with 1-2 Zone-4 efforts at the end is enough.