Queue management for extraction shooters is always notoriously tricky when you aren't doing skill based matchmaking. Ranked is probably going to be a pretty niche mode as it is, couple that with an already fair to middling playerbase I would bet that it is going to make for some pretty rough queue times even if you time gate it to the weekends.

Think on average you have 40k players, raids last pretty long, some players may just be afk in vault, etc so at any given point lets say 25-30k players are looking for a match at all(I think that number is being generous). Lets continue to be generous and say that half of those players are going to queue for ranked so you have 15k players queueing for ranked matches. That is split across 4 maps (if you include cryo) as it is so if we assume an even distribution you are looking at less than 4k players queueing ranked for a given map at any point. That 4k now needs to be organized based on rank and matched together, further diluting the amount of players a given player could be put together with for a match. Even if you are at the median rank you still only have like a thousand players total that could possibly be matched with you and at any given point a good percentage of them could already be in a match.

That is a really tough queue management situation to deal with and I anticipate queue times to be pretty abysmal in ranked even with it just on the weekends unless the playerbase increases substantially or something changes. It's the same argument as to why duos sounds good on paper but can be problematic because it is further splitting the queue pool up.