For me between 6 min and 1 hr. I have a tube integrated and it takes about 6 min for the tubes to get the bias up. After an hour they are fully warmed up. The difference between the 6 min mark and 1 hr is hardly noticeable.
How long it take before your system/amps sound
...the best. My system sounds the best after 12 hours of playing. I didn't realize this until I inadvertently left my system on overnight. I was surprised how much better it sounded compared having the system on for an hour or two. I have tube DAC and amps, which probably are the reason for long warm up. His really surprised me.