I think this really depends on the code base. If I had a website where a change would trigger more than 5 minutes of integrating and testing I would go mad.

I'm working with a weather model and it takes around 1 hour to build and test everything: We build against 2 super computers, 3 different compilers, 2 different architectures (CPU, GPU) and single and double precision. Building alone takes 30 minutes (more in some cases). For testing we reserve 1x node with 8 GPUs and 9 CPU cores on one machine and 2x nodes with 1 GPUs in a 30 minutes debug slot.

With a pull-request based workflow we are able to push to the master multiple times a day. 40 minutes might be achievable by massively revamping our build mechanism and getting jenkins to store gigabytes in build artifacts for each run. However, I do not think it is worth it, because changes can take multiple days, or in some rare cases months to implement. If people need to wait for an hour for their tests to validate that's not so bad.