This issue is related to your password. Your password is case sensitive and if you don't enter it EXACTLY as you did when you registered, it won't let you in. If you make five attempts and don't get it, you get locked out.
This has no bearing on the time of day or computer that you are on. It is a necessary security component.
The reason this is done is because computer bots will hit the board constantly trying to get into any member account so that they can post spam. It is a big, big problem for sites of this type. With four forums like this one, we deal with the issue on a daily basis.
Thus the measure. It isn't there to aggravate you, it is to protect the board.
This kind of thing usually happens when you log in and check the "remember me" box -- meaning that the site will remember who you are on the computer you originally log in from. If it is the same computer and you come by nearly every day, you could go a long time without ever having to remember your password.
So if you clear your browser cache or try to get in via another computer it is possible, because you HAVEN"T had to use your password for a long time, that you input it slightly off from what it really is, you try five times and it locks you out.
I'm guessing this is what happened in this case. I would recommend that you go to your User Control Panel and reset your password and make a note of it somewhere so you don't run into the same problem down the road.
Jeff