Actually, if you're only interested in the page load times (and not the asset timings), the call should just be:
s.performanceTiming()
You should be able to read the contents of the cookie (where the timings are stored for reading on the next page) by inspecting it in the Console before navigating:
s.Util.cookieRead('s_ptc');
Should look something like this:
"0.00^^0.00^^0.00^^0.00^^0.09^^0.00^^6.25^^0.01^^6.36"
If that cookie's not being set, you've possibly got a timing problem (we had this on our site and had to modify the plug-in and the code we added to s_doPlugins).