No problem! Can 2 or more users buy a slot simultaneously for now(till automatic option's integration)? Either automatic or simultaneous-buying should be there, automatic is better IMHO. There is no need for this option for time-period-base-buying but for CPA and CPM, it should be there. Otherwise, advertisers will have to wait till the number of impressions and/or clicks reach to buy it and if it is like that, it would be based on pure luck as there will be many others for advertising. So when there is simultaneous-buying, the ad can be shown according their submition order.

BTW, in post number #6, you typed CPA two times.

   ~~MZ~~