First of all, you have to specify full path, not just Temp. Second, you have syntax errors in recursion and size parameters - you should use only digits here. So, parameter should looks like
File.Count('C:\Temp', 'SAS*.txt', 1, 0, 90)
to count number of files older than 90 seconds.
Then, threshold by itself looks correct, but did you create appropriate rule in event processing policy?
Also, take a look at this step-by-step configuration example: https://www.netxms.org/documentation/confexample/. It's quite old, and screens will look a bit different, but you should get an idea.
Best regards,
Victor