You can now display your local timezone on your profile to give others an idea of when to expect responses to pull requests or issues from you. You can opt into this feature by navigating to Settings > Public Profile and checking
Display current local time. You can also update this information directly from your profile by clicking 'Edit Profile' under your avatar.
This will display your timezone in the left sidebar of your profile as well as your timezone's current deviation from UTC. When other users see your profile or user hovercard, they'll see your timezone as well as how many hours behind or ahead they are from your local time.