Both of them represent the actual time at the moment of their evaluation. However, REALNOW returns a value of the actual time and date together, while ESPATIME returns a value of actual time only, then ESP uses the application generation date to get the completed timestamp.
NOTE Keep in mind that when you use these variables within the free-form time criteria, an unexpected result may happen. For example: LATEEND('%ESPATIME PLUS 15 MIN') might bring an unexpected result into the application that has been active for more than one day.
In other words, the result of the REALNOW variable, will always be the same as the ESPATIME used in conjunction with the ESPADATE %ESPADATE%ESPATIME equals REALNOW but %ESPATIME equals REALNOW if it is evaluated the same day that the application was generated only.
This Frequently Asked Question applies to all supported releases of ESP Workload Manager.