The system was launched by the county council in March after a huge increase in demand led to congestion on several major roads, with queues causing problems for residents and businesses.
The system, which has been trialled at Bognor Regis, Crawley, Horsham, Littlehampton, Shoreham and Worthing, is due to be reviewed on September 30.
A county council spokesman said: “The booking scheme has been popular with residents and delivered a range of benefits, including reduced traffic queues at busy sites, improvements to local air quality and more people being mindful of disposing of waste, for example bringing more waste, less often – offering greater environmental benefits.”
So far, 325,000 bookings have been made for slots up to October 6, though 13,000 of those appointments were later cancelled.
Fewer than six per cent of people failed to show up for a pre-booked place.
Of the six sites, Worthing was the most used, with 86,769 bookings, followed by Crawley with 72,080, Littlehampton with 47,046, Horsham with 46,442, Shoreham with 31,653 and Bognor Regis with 27,863.
Between April and July, this saw more than 35,000 tonnes of rubbish and recycling dropped off.
The system will be reviewed at a meeting of the Communities, Highways and Environment Scrutiny Committee at the end of the month.