That's something I've been curious about: Do you have to read the signpost to get the MotD benefit, or is it always on?
I am not sure because a trophy is linked to going up to the sign the first time. Someone needs to test if it works offline that hasn't gotten the trophy yet to confirm, if it still works when not connected online.
FC: 4940-5524-8052 "A delayed game is eventually good, but a bad game is bad forever." - Shigeru Miyamoto
You can change the clock on your console to fool it into thinking it is a different time, you know.
I did that once with my PS2 and screwed up several different saves of several different games. Never touching my console's clock again. EVER.
There's an achievement/trophy in Nier which requires you to tend to this garden a few times (I can't remember exactly what you have to do, I think you need to create a certain flower). I don't really like messing with the system's clock either.