That delay is usually due to latency either between the player's PC and the site, the current load on the VTT's supporting servers, or browser performance. Some browser extensions can also cause delays, especially some VPNs, ad blockers and anti-malware apps. Very large or very busy maps will also degrade performance. I recently ran (well, tried to run) a large scale battle with almost 100 tokens on a 65 x 65 grid square map with a few scattered dynamic lighting barriers. When it was just me as GM setting up the map, performance was OK, but as soon as my (5) players logged in the lag became so bad that the scenario became unplayable.