Usually "Units" refers to a period of time indicative of the micro controllers clock speed. For example, if each cycle (command) takes 1uS to execute, then 1000 units could equal 1000uS.
That said, with higher languages (such as C, Basic, Pascal), its not usually a 1:1 basis, but rather somewhere in the realms of 1:5. For this example, that would mean that 1000 units would equal 5000uS.
This is just my interpretation, I'm sure either the help file or practical testing will be the easy solution
BTW, commands such as these are usually capped by the variable type that the macro/procedure is limited too. eg, if a word then the maximum value would be 65535, and 255 for a byte