12v 20a lead acid battery charging time?

[waztrain]

Hi

I have got myself a 20a lead acid battery(golf trolley size) to use when I am at the track. I got myself a wall 500ma charger. I just wanted to know how long it will take to charge full from flat? I have been told by the seller that it will take around 30hours. I just want to confirm this as I feel abit uncomfortable leaving a battery charging for 30hours.