Modern computer programs are more complex in writing and more difficult for reversing. Serious programs have various means of protection against debugging. It prevents application reversing. There are a number of various approaches, like Debug Blocker, Nanomites, others.
Measuring time to identify that an application is being debugged becomes the widespread practice lately. The OllyDbg has the HideOD and Hide Debugger anti-debug plugins, which have no possibility to hide actual time. This causes difficulties in application reversing.
Let's consider the system of debugger identification. The debuggers are capable of making breakpoints in code. In this case the operation of the program is suspended. The program can detect such stopping by monitoring the system time. If there is a too long pause between the instructions - most likely the program has been stopped for analysis.