It is simple math: your job requires 8 hours of work (really 6.5 with breaks, relationship building, non-work tasks at work) and you don’t have extra time in the day. Since you started or since your company came up to capacity you have never had the occasion, say around 3:30pm, to say, “I have nothing to do but rearrange the break room cupboards.”
Knowing this is the case, that no one has extra time, how can you expect to implement a change without doing one of two things:
1) cut your regular work day short by a few hours, and test the rest of the time, for instance
2) work beyond 8 hours, with overtime pay or comp hours
Time and time again, I see managers try to cram UAT activities, data migration/report reviews, and other time consuming requirements for a project into a regular workday, with no consideration for the extra time it takes to complete these important activities.
Once, while consulting a project, I was asked to determine why a report from an implementation the year before by another firm was not matching the data entered. Turned out no one completely confirmed the report field by field to ensure it was working correctly. The company culture, always molded from the top down, did not allow for the extra time needed to ensure the software implementation was completely successful. Saving money was their goal.
You are kidding yourself if you think you can just “fit in some time later” to do the extra and necessary work an implementation brings. Often a temporary staff to do day-to-day operations so the regulars works can confirm you are getting what you paid for and it works for your organization as planned.
Short changing this process is just asking for a bad result, rework, and voiding your warranty.