thanks for asking.

The key presses should be instant (unless you mapped a different 
action to the hold states of the respective buttons). RC2's mapping 
algorithms actually have been updated to allow instant presses 
without any unnecessary delay.

My guess is that it's simply a performance issue. You might want to 
make sure the IR mouse mode is turned off at the time of use to avoid 
any unnecessary event traffic during gameplay. The performance of 
your system could also be a possible cause.

Also, you might have set "Send keystroke on release" in your actions, 
which would only send a keypress at the time you release the button.

Best regards, 
Felix