Where does my negative input voltage come from?
Do you want the output of the op-amp to exactly follow the output of the 555 timer? 

Either way, I think you might be confused about how an op amp works. They have extremely high gain (think 10,000 or greater), where the output is that gain times the difference between the "inverting input" (marked with a "-" in diagrams) and the non-inverting input ("+").

I don't think you want to simply connect the "-" to ground; it would act like a comparator, such that when "+" is taken above ground, the output would saturate high, and when taken below ground would saturate low. 

Instead, connect the "-" to the op-amp's output. This creates a unity gain (gain = 1) amplifier. The output will then follow the non-inverting ("+") input.

If you don't want a unity gain follower, you can use resistors to set up different gains, subtraction/addition, and more. 

One final thought - what are you connecting to the output of the op-amp? What rails will your system use? (Eg Ground and +5v). An op-amp might not be the ideal choice. Their output current is very limited (less then a 555 timer usually) and their outputs often don't saturate rail to rail (although many do - but I'm just letting you know to avoid a "gotcha")