The delay is at least one agent interval, normally 1 minute. If the check runs longer than the interval, the data is simply transmitted in the next following agent run.
12:00 Agent run
no cachefile found, start new check in background
12:01 Agent run
print check result from 12:00
12:02 Agent run
print check result from 12:00
12:03 Agent run
print check result from 12:00
12:04 Agent run
print check result from 12:00
12:05 Agent run
print check result from 12:00
cache is outdated, start new check in background
12:06 Agent run
print check result from 12:05
...