Theres two ways of posting your mixes on this site. The 1st being via the forums, where you post your link as you've said but, the 2nd is within your Dj Profile - there you put direct links to the mp3s themselves, as opposed to links, which are not allowed. The time taken is for our friends at BanginTunes.com or perhaps, a slow to react computer, which validates the mp3 link. The advantage of doing option two, is that you get a hit counter for each mix (mine stands at over 2000!!)
The disadvantage of option two for me is that my hit counters on my own site wont register a direct download of the mp3 - so my hit counters are about 2000 too low !
Steve