1. According to this paper, the grapevine protoplast cell wall formation was studied using Electronic Microscope. Please take a look the nice pictures.
"Results showed that microfibrils were developed after 2 days of culture, that complete cell wall formation occurred on Day 6 to 7 of protoplast culture".
2. From my experience on tobacco protoplast growing, protoplast cells start to divide within 7-10 days. So, the time for cell-wall formation of tobacco protoplast seems to be similar to the time mentioned in the attached paper.
Yes. And the cell-wall forming time of protoplasts might also be affected by the tobacco varieties used, such as BY-2, Wisconsin 38, petite Havana...etc.
The previous answer I gave was based on tobacco Wisconsin 38 and the protoplasts had been treated with chemical PEG for transgenesis. The treatment (PEG), solution washes and transgene overexpression (caused metabolic burden) might have affected the fitness of the protoplasts. At 7-day, we observed a new protoplast attached to the old one, which indicated cell wall might had formed before 7 days.