The restrictions are only a temporary measure whenever a server's starting areas are incredibly congested to make sure that they keep running smoothly. They actually open and close based on player population in the starting areas. The Lodestone site updates the server availability list every 4 hours but some servers have periods of being open in between the 4 hour list updates. If you try to make a character during times when many people are likely to be on (say, evenings during the weekends) then you will very likely be locked out.

I would advise you to make your character in the early morning, it seems to be the best time for servers to not be congested. I have had over a dozen players join Hyperion, which is in the same situation as Excalibur, and no one has had any issues in the early morning. Late night would theoretically be OK too but more people play at night than in the morning.

My brother actually just started playing this evening and at around 9:00 PM the server was restricted. At 10:00 PM the status updated, it was open for new characters, and he was able to start playing just fine. Just try again later.