Doing it monthly makes it pretty easy for me to not "be behind".
-- I collect my pictures (and ephemera) over the course of a month,
-- make daily notes in my calender (I did keep a "notes journal" about the main activities of the day since my 12 birthday anyway, so this does help with my PL a lot),
-- then order prints and
-- spread them out to fit x full pages, not even spreads. That way I always have the freedom to have my PL according to what happened or what pics I have. I try to keep fotos of 1 event together and have it all more or less chronological, but shuffle random fotos (of a pretty flower or morning coffee etc.) around if I need (for the flow or because of colours).
This works for me since I started in January and never gave me any pressure, au contraire, I look forward every month to get new prints to play and do my PL and new LOs with last month's fotos.
It does take me 1-2 evenings though, but I enjoy those evenings enormously.
Maybe those of you who feel pressured with their PL (which ist kind of ridiculous, because PL was intended to be the solution to any "scrapbooking pressure" -- a concept that I do not get anyway) should try to do it monthly. It is probably harder to find 1-2 evenings a week for the PL of the last week than doing it every 4-5 weeks in about the same amount of time.