That is a hard question to answer because turning a bowl or other woodturned items is a staged process. Typically for my bowls, it takes a bit of time to source the material i.e. the tree might need to be found and felled, then cut up into manageable pieces for transport back to the shop. Once on my property the log or blocks might sit outside for some months before I get to them. Sometimes this is done on purpose to allow the wood to spalt and develop some interesting colour and patterns. When I am ready to process the log, individual bowl blanks are cut to length using a chainsaw and then those blocks are cut in half along the wood grain or cut into multiple pieces to deal with flaws or design features. The pith or centre of the tree section must be removed to avoid the cracking that would no doubt result from this section of the tree. Often I will coat the ends or sometimes the entire block of wood with a paraffin wax emulsion to reduce pre-mature cracking of the wood. Each block is then cut to a symmetrical turning blank (round or square) using my bandsaw. Again, if the pieces will not be worked on soon, I will either coat them with sealant or store then for a short period in plastic bags or wet sawdust to slow the drying process and reduce cracking (checking). Once I have a number of prepared blanks, the pieces will be rough turned on the lathe to a greater thickness than the final product. The rough turned pieces are then sealed and set aside to dry slowly in a cool, shaded area for one to two years depending on the thickness of the piece. Rule of thumb for air drying a bowl blank is one year for each inch of bowl thickness. Bowls will warp and become out of round when drying (hopefully will not crack but that happens too) and that is why the rough turned blanks are thicker than the finished piece. You need the extra thickness when doing the final turning so you don’t run out of wood! When the bowl blank is dry enough, usually less than 12 % moisture content, the piece is put back on the lathe for final turning to thickness. The bowl is power sanded on the lathe and then removed for applying a food safe finish. At least 2 or more coats are required and the finish needs some time to cure before the bowl is ready to sell.
To make a long story short, a bowl can take from one to three years from start to finish. Actual turning time on the lathe accounts for a small fraction of the time, anywhere from 15 minutes to a full day depending on size and complexity. Of course if the bowl blank is purchased from a supplier and the blank is already dry, the time for me is reduced greatly but I prefer preparing and turning my own blanks. It is much more enjoyable!