you can get the runtime of a process with this subroutine
get_ProcessTime("iTunes")
on get_ProcessTime(proc)
try
tell application "System Events" to set pid to the unix id of process proc as Unicode text
return paragraph 2 of (do shell script "ps -p " & quoted form of pid & " | awk '{ print $4 }'")
on error
return "0"
end try
end get_ProcessTime
but I guess, the returned string has a special format (not just mm:ss)
you probably mean
ignoring application responses
-- do something
end ignoring
default is considering, that means AppleScript waits for the response of the application