For example: I would like to put validation on all responses to indicate success if response time is < 4000ms. I know I can set a response time validation on each individual request, but am hoping there is a better way to do it in just a few steps.
The global validation feature exists. It can be done at the virtual user level.
In design part, select your virtual user profile and in the right pane click on the "Global validation" button.
You may have to configure on which responses you want to apply your validations based on their content type.
For more information, see "Requests" under Design section in NeoLoad documentation.
Sorry, i did not realize that you wanted to validate the response based on the time duration.
Unfortunately, this option is not possible. You can only create a global validation based on a text content.
I would suggest you to create a new idea so the developers can enhance that feature for future NeoLoad version.
SLA Profiles feature has since been introduced and provides single point of control to check that avg response times across all virtual users (all requests) do not exceed a given value.