You can install Luna here. There are two ways to interact with Luna, Slash Commands and Bot Mentions.
/luna [@user] - Will return the current local time of that user.
/luna [city] - will return the current local time in that city.
/luna [time] [city] - Will convert your local time to that citys time.
/luna [@user] [@user] [time] - will convert your local time to each users local time.