I’m glad that worked! =)
This is old and marked as answered - but comes up first in Google, so just to add a comment.
Originally the poster here (the Op) was using Add Actor Local Rotation, his fix was to use Set Actor Rotation - this answered the question, but did not suggest why the former did not work. I have noticed to a bug with Add Actor Local Rotation when it reaches 90 (goes from -270 to +90), in theory it should flip to -270 at 90 so it can continue to add, but as of 4.5 it does not, it just stops adding!
Added post here: Add Actor Local Rotation Bug - Blueprint - Unreal Engine Forums
Awesome to see that you got this working.
My method for doing this is to use Get Game Time in Seconds instead of dealing with adding the Delta Seconds per tick. It cuts the Time Float Variable, the Add and the Set Time Float out of the equation.
Wondering if this is a bad way to do it, since it did’t get mentioned. Anyone have any insight on this approach? Still learning myself and am always up for tips.
Seems reasonable to me - assuming that you do want from the game starts and not some other starting point (because then you would be back to maths per tick). Of course, behind the scenes, Get Game Time is just keeping count of deltas since the game started 
- but only doing so once.