Can I make wine from the fields I harvest with the Laborer?
Yes I believe you can. 

The rules for visitor cards state


  Many visitors have two separate clauses delineated by the all-caps
  word "OR".  These are two completely independent clauses.


, so in a normal situation you can do just one. However the Labourer is giving you the option to do both so there is no reason why you couldn't do both and thematically losing a point for the labourer to work extra hard makes sense.

When you harvest you add grapes to crush pad.  When making wine you move from crush pad.  There is no rule that says they have to be there a set time limit before they can be made into wine.  There is nothing on the labourer card that says if you choose to do both they happen simultaneously.  You would choose the order they happen in to your advantage.