I have heard that the earlier you complete online check-in the more likely you are to get your room amenity requests. However, this is what I have read - not sure how true it is. I always choose my room to be ready over any amenity requests. I also have always put a realistic time I would be arriving, and all my trips, except maybe three, I was able to receive early check-in.
Not sure which in-room celebration you are considering, however, I have been on the receiving end of a few in room celebrations. The best has been one DH did for our anniversary. It was the one where you got roses, rose petals around the room, gift basket, bath towels, and a few other items. It was truly special to walk in our room with it all set up beautifully. However, DH told me after the fact that he couldn't give a specific time it was to be set up, just a time frame. I have had a few other celebrations with their flowers, and they have all been gorgeous!