How long do you have to play (In weeks) for max Friendship level up to 20?

[Enfyny]

It allows you to complete 2-3 quests WEEKLY! before waiting another week. Do you have to play like year or two to maxing it out?

[KYORO CHAN]

To maximize a character's friendship level, you don’t need to play for an entire year. For most people, three months should be enough.
However, the friendship level between players in online multiplayer mode takes about six months.

[Enfyny]

yep, i was talking about the multiplayer. But six months...