PM 75, when the OS increases, that is the date the conversion is registered and recorded as part of the new share count. Thereafter, the holders of these new shares have the right to sell or hold as whenever they choose. They could sell immediately or wait till the next day/week/year. They do not have to sell at the time of conversion.
Important to distinguish between conversion and selling, they are two separate actions that do not necessarily happen concurrently or consecutively but can.