Not by using the /fx commands. While the MetascriptToolbox offers a {&delay} command that can delay chat commands if they start as an API command, by doing that to an /fx command, there is no player owning the message AT THE TIME Roll20 wants to process the /fx, so nothing happens. Theoretically you could do this if you had a script that was spawning the fx (there is a command a script can use to generate the effect). Then you *could* use the {&delay} tag to slow the second one down. I'm not aware of a script that does this (narrowly), but it wouldn't be hard to write one. I think.