No problem with the English: it is not my primary language too. 
Where did you put the timer block? Usually you have to put in "when created", because if put in "always" it can give problems.
Have a look here:
http://static.stencyl.com/pedia2/blocks/flow/flow_time/periodic.html
for the correct use of timers (under "Advanced Uses" there is an example similar to yours).
I was trying without "created". I was using the: "Add Event / Time / Every N second".
So I deleted this one and create a Basic / When Creating event, with your round block.
And my timer it's not working.
My timer is a Scene Behavior with a attibute time.
I think Stencyl need to upgrade the help section with this kind of solution.
If it's an inherit limitation of floating point numbers maybe a official explanation on the Help page will explain a lot for the new users, not programmers like me.
Thanks Nev, I'm gonna check your link right now, and Sunflower post, if I suceed I'll post the full design block here, for future users.
I'm building for iOS.
-------------------UPDATE-------------------
So I'm trying with 1/10 and no luck.
Gonna try with a text [number without last digit] + "." + [last digit].