Timestamps for messages

I'm using firebase's database to host a real time messaging web app. I've finished the basic implementation but now want to add timestamps for users to see when messages were sent.

To add a message to a chatroom I use firebase.push() with the value as the sent message. I guess I'll have to switch this to .update() with the value as an object with the fields message and time sent.

I'm trying to figure out how to populate this time sent. I've heard of firebase.database.ServerValue.TIMESTAMP but from what I can tell it's hard to change that into a date and time. I'm heavily considering a unix timestamp like this var unix = Math.round(+new Date()/1000); since this is easy to convert.

Does anybody with any experience have any tips for which direction I should take? I don't need the timestamp to be super precise, just the date, hour, and minute.