How to collect data for dissertation if the work wasn't published I'm starting my dissertation in which I'm creating a mobile application for public use.

My problem is I need evidences to support my hypothesis and I was informed
that I will only be allowed to collect data from users inside the company
for which I'm doing the app, since the application won't be released in time
of my deadline.

I think this might invalidate my data since these are users who are aware
of the application development.

I thought I could do some quizzes and try to have "outside" people to fill them
but I'm not sure if this enough to support my hypothesis since these people
didn't had any contact with my application.

So my question is if using data from quizzes about a possible solution (like
mine) is enough to support my dissertation since I can't let people try my app
by themselves.
Very hard to answer without knowing the details of your work, the app in question, more background, and what other contributions you can make part of your dissertation. But… even if a formal release isn't possible by the deadline, couldn't you arrange for testing on outside people but on your devices (instead of theirs)? That way, you can load the app on a series of say, 10 devices, then have people test it (sort of a focus group)…