Yeah, It's more a matter of who and what, not when.

They do like to see letters from people of substance, ie employers, military CO's, even civic or church leaders as that speaks to aspects of your character beyond aviation monkey skills.

But they also expect at least a couple LORs from pilots you have flown with, ideally CA's or CP's, although letters from previous FO's is fine (especially if they now work where you're applying... BTDT). Non-pilots can attest that you're a great person, but cannot address piloting skills and should attempt to not do so (unless maybe you worked for them as a pilot). Letters from pilots should always attest to your operational emphasis on safety.