hey mama, i had my lo on a 'routine' as opposed to a schedule. In my mind a schedule sets up unrealistic expectation and can create inflexibility. Whereas a 'routine' lowers expectation and allows for flexibility. It helped a lot. I based the routine on what cues he displayed. His routine began when he was 8 weeks and was a three hour one, with eating following sleep and activity following eating. ie: up for the morning, eat, play, nap, eat, play, nap, eat, etc...). The time of the activity didn't matter, but I did observe length of time . I didn't care at what time he played, but noticed that after an hour of activity (including diaper changes, etc) he would start showing signs of tiring, which would cue the nap. His routine helped because I learned a lot about his needs and how to curb upset. For example, before the routine, I didn't pay attention to naps either, now I know that if he doesn't get at least 4 hours total of naps in a day, getting him to sleep at night takes longer because he gets overtired and fussy. As he gets older, the length of activity increases as he can tolerate more.
Be realistic. 12 weeks is still young, but it is possible to observe LO's needs and create a day that gives him/her what is needed without being harsh. It may take awhile to get the hang of reading LO's cues, and it might need constant adjustment. For example, this whole post is in past tense because LO got sick and I needed to start letting him nurse as he needed to soothe him, which threw the previously established routine out the window. Now he's better but got to nursing himself to sleep, so I'm letting him until he's ready to stop again. The routine is changing because he changed, but I know that he still needs a certain amount of nap time to be healthy, so I'm focusing on making sure he gets that while we figure out the rest.
Start with observation, and what he needs will make itself known! Good luck!