Bonjour Clarissa !

The word "tôt" means "early" as opposed to "tard" (late) in French, to indicate a time in the day, i.e. "early in the morning". 
e.g. "Je me suis levé tôt."    (I got up early.)
       "Oh là là, il est tôt !"     (Oh, it's early!)
       "Tu es arrivé plus tôt que prévu."   (You arrived earlier than expected.)

"En avance" and "en retard" indicate a relationship between those moments and a given time: you're early or late compared to that given time. 

I hope that's helpful!
À bientôt !