What I see from your screenshot is that you are not using the handle itself. You should set the return vale of ‘Set Timer’ to a variable that you will then use as the input of the ‘Is Timer Active’ node. You would also clear the timer the same way, just through the handle:
http://i.imgur.com/O2juaEx.png
NOTE: You may have to check if the timer is NULL or play with the IsValid function