Just want to mention, my suggestion for NOT using 1:1 time wasn't actually intended to include any fancy maths or calendars stuff, just a general guideline of "don't advance time faster than x" or such and letting it flow naturally. I've seen it done that way in another game (here is an example) where all posts were tagged with a tag that indicated what set of days they were to make it easier to navigate posts by IC timeline. When in-game events were announced people would inform when it would occur OOCly (e.g. "this Friday") and occasionally give an IC date if something time-sensitive were going on (e.g. "on Day 200 there will be a thing so DO NOT ADVANCE PAST 199") but otherwise just assign an IC day to the post as appropriate.

So unless months and seasons are of particular importance to the setting this is the model I'd recommend using. I've seen it in action before and it made it REALLY easy (at least from a player's perspective) to keep track of what was happening when.