It doesn't really matter whether you check in online or check in in person--either way, your rooms are assigned 5 days prior to check in--the front desk is just telling you where the pre-assigned rooms are. Connecting rooms is not a bookable category, just a request, so it's possible your rooms won't be connecting and you'll have to go to front desk to see if it is possible--though if you have the request on file (i.e., you or your
travel agent has called in to request it) and it has not been honored, online check in vs regular check in is not going to increase or decrease your likelihood of having your request honored. If you get there and you didn't get what you want, you can always go to the front desk and ask even if you checked in online, but at 10pm, odds are most rooms are going to be occupied at least for the first night.