One hour for sure, perhaps even longer. Seems to sound awesome after a few hours, but by that time my judgement has usually been impaired by a few beverages.
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.