I might be the wrong person to ask because I am a Persona and SMT fan. Metaphor is easier than Persona is what I feel. Since u asked about time, it's a long game. No matter what, do not rush as you will tire urself out.
Also if you have never played Persona or smt, it will take some time for you to get comfortable with the game. Do not give up if you don't find it likeable in the first few hours because it takes some time to kick off.