You have already sent out an RFP (request for proposal) for a laboratory software and have received several responses. Regardless what the vendor provides, you need to contact a comparable site to your own and assess how well the solution is working.
The key word is COMPARABLE. The site should have similar functionality (breadth of test and process menus), test and activity volume. If you have multiple sites, does the candidate site have the same?
Technically, to assess response time, you should select a site that uses the same platform (e.g. Microsoft SQL Server, Oracle, etc.) and operating system (Windows, Linux, UNIX, etc.)
At one institution I worked at, they went on a site visit, but it used the software on a different platform (UNIX). They wanted to use it on Microsoft SQL Server. They were happy with the observed response times during the visit, but when they installed it on their chosen platform, it was very slow. You cannot compare an apple to an orange (or in this case to a prune).
I would ask to speak to key players at the site visit without the vendor being present. Hopefully, they will be honest with you about their experiences. I was once very surprised that I was asked to allow for a site visit for a non-blood bank software for which I had serious concerns. I would not serve as a site visit.