Presentation Timing Is Delayed on PC Laptop not Mac

I am in the process of writing a program that should flicker between two stimuli. I created a very simple set of trials that just alternate an “x” an an “o” every 34 ms. (Each stimulus presentation after 34 ms). The draw time for each of these is negligble (approximately 0.05 ms).

I programmed identical programs on a Mac and PC. On the mac, it appears to work as written. However, when I run it on a Dell Vostro v13 Laptop (60 Hz refresh rate), the presentation was significantly slower. There is no differences in how the two programs were written. Is there any known explanation for this timing discrepancy? Is this a difference between Macs and PCs? Or maybe because it is a laptop? Any help would be greatly appreciated!

Hisham helped Chris resolve this issue. Please let me know if you have any follow-up questions.