This isn't actually true, though, at least for Moderna and Pfizer. All the Phase 1/2 trials ran for normal lengths of time from the medication followup period side of things, Phase 3 got split into two, one for emergency use, one for full approval (this followed standard followup timelines), GCP oversight was in place, etc.
What really allowed them to rush to market was the timing of other things around the trials. Normally there is time in between the trial phases, but for the covid vaccines, as soon as the data was compiled, the next phase started. This cut quite a lot of time off the process.
The other thing that cut major time off the process was starting mass production during phase 3 trials. With world governments footing the bill, the companies didn't have to risk the financial loss of throwing it all out if things went wrong in the p3 trials. So as soon as the p3 trials were concluded and the data was in, the FDA could use it for emergency use authorization and there was a supply ready to go.
Trial length was compressed as well, but largely not in the way most people think - the follow up time period for phase 1 and phase 2 after vaccines were administered were the same as you would see in any vaccine trial, but the increased speed on all of the administrative tasks cut down trial length. Phase 3 was initially shorter - 2 month follow up time - for the emergency use authorization, but full approval was still received after the standard 6 month followup. Counterbalancing some of the rush for the EUA, they did enroll a fuckton more people in the trials than standard vaccine trials. Like 70k between the two for phase 3 vs. what normally would have been 10-15k between 'em. But they passed the follow up at 6 months, to