How are you scheduling downtime? Manually through the web GUI? If so, I don't see a way to accomplish what you want.
An idea is to write a script that would schedule a downtime through external commands (here I took an example of scheduling host downtime):
nagios.org/developerinfo/ext ... and_id=118
and then also add to the script the external command to issue a check or whatever you wish after scheduling downtime (here I used force host check):
nagios.org/developerinfo/ext ... and_id=128
You combine those two scripts into one and then you have scheduled downtime and after that scheduled check.
You can run the script through crontab or manually when you wish to run it.
Hope I have understood well what you're trying to achieve...