Didn't see an answer to this one (but apologies if i missed one), the smelters are grouped together, so you have used your smelters for 62 hours in total, that may be 40 hours on 1, and 22 on the other for example. They will upgrade at the same time. The other inconsistency I don't know, but I have heard that using diamonds to speed up a production gives the hours to the mastery, i.e. speeding up a 3 hour juice with diamonds adds 3 hours (though I cannot confirm that to be true)
interesting