See PHI615. Ref T13130. An install is reporting that "Lease Working Copy" build steps always report "Built instantly" after completion.

I'm not 100% sure that this is the fix, but I'm like 99% sure: "Lease Working Copy" build steps yield after they ask Drydock for a lease. They will later reenter doWork(), see that the lease is filled, and complete.

Right now, we reset the start time every time we enter doWork(). Instead, set it only if it hasn't been set yet.

This is low-risk and a bit tricky to reproduce locally, but I'll run some production builds and see what they look like.