What is the best way to approach PRs with long build times?

I am curious if swift: 5.1.1 -> 5.4.2 by trepetti · Pull Request #132325 · NixOS/nixpkgs · GitHub should target staging instead of master. The validation tests are actually important for picking up regressions between versions in packaging but they just barely go over ofborg’s 1-hour default timeout limit on x86-64. Arm machines can’t even finish the build itself within an hour. If I target staging, would the CI go through Hydra instead with a longer default timeout?

This post is what motivated the question. I guess at one point, Chromium builds had a similar problem. The issue with Swift is that it needs to compile its own modified version of LLVM and Clang before it can even start to build itself, so there are a lot of serial dependencies in the critical path.