10-11am GMT is a good time if you're looking to target the prime English market of video creations. 6am EST is the approximate equivalent, and targets the morning of Americans.
But it actually mostly applies to where the most of your consistently viewing subscribers are found in the world. If you have a mostly British audience, then uploading at 6am GMT would get most of them. Up until then, uploading at particular times doesn't really do too much.