Maximum frequency measured by STM32F10x
Whatever the internal bus speed (HCLK) determines the unit of time you can measure. The max is 36MHz but this will depend on how you have configured the clocks and prescalers. Only 16-bit timers are available on the F10x line. 

So 1/36Mhz = 27.777ns

The max time the timer can measure in this mode is: 27.777ns*2^16 or 1.82ms