The current wiki page under "Notes" at the bottom talks about what affects mining speed. One thing ive noticed is that as I mine, over time my first action take more and more time.
At first I thought this was water but sitting for some time afk so my water bar gets low and comparing my first action (with full stamina) with full and half empty water bar makes no difference to my first action timer.
I have observed previously also if start mining with a full food and water bar at I have a 3 second action timer. As time goes on that while mining, my first action (with full stamina) timer gets longer, seemingly as my thirst level increaseswater or food bar dcreases. If I drink water, it goes back to 3 seconds.
Could this mean that water bar /food bars and perhaps fatigue are related to action timer?