What has accuracy got to do with it, it isn't really encompassed with the present system when you consider the -5 +10 dimension. There would still be the same number of aircraft and they would fit into the flow in a random manner.
If i can tell you about my flight yesterday. I had a slot delay of 55 mins, for destination airport restrictions. I was a/b on the CTOT, my sid should have been about 75 miles of meandering thru the TMA but i didn't actually fly more than 3 miles of it as i was cleared direct to FIR bdy (about mid point of the journey). I took a substantially lower level than planned to make use of 130 kt tail wind. total time savings were about 27mins, and this is out of 55 mins where technically my destination didn't want me there.
From FIR Bdy i was cleared direct to centre fix , speed restrictions removed during decent and i was only taken off that route to be vectored number one to a 5 mile final, if i hadn't of bounced it, it would have been a great day.
The CTOT system came about from the original regulation system, like i said earlier but that system began because of some pretty awful European situations, with closed airspace, strikes, poor equipment etc. I don't think that exists today. I think it doesn't matter where you apply the restriction the fact remains that the number of aircraft in the system will be a constant and whether it takes 5 mins or an hour to get away just adds to the randomness of the distribution for the area controllers to deal with. In my experience, and i do have some, controllers work harder and enjoy the peak rushes far more than a constant, never ending stream across their tube. The problems only occur when the constant stream is a peak flow. This we shouldn't allow and hence the need for regulation.
In addition to that we've lost the benefit of the 'NO DELAY' option.
Lets say I'm at a busy airport in peak. My company request a CTOTwhich is EOBT +25 (knowing there is no way i'm going to get a/b in less than 20 mins)
I call for push on schedule and ground fit me in to the system. Now heaven forbid i do that in off peak time because the controller would look at the traffic and say i was too early (ie; a delay) or to put in a ready message. All of this takes time and my opportunity for schedule is gone. Now it may only be a couple of minutes but those are the minutes by which the CAA and the various transport users associations measure our performance.
The long and short of it is that if you were allocated a CTOT as you requested and a ready message again gets you what you want then it should have been NO DELAY all along. I could even accept No Delay until xxxx time.