Ann: Cleansing Notice - Options Conversion, page-6

ASNOC and ASNOD can both be exercised at any time up until expiry and yes it can take up to two weeks depending on the company, some do it quicker. If you don't exercise them and can't sell them on market before the expiry date they expire worthless. They company doesn't buy them back. You would have to weigh up the number held, how much you paid for them, how much they are worth, the total exercise price and if you think the share price will appreciate in the future when deciding if it is worth exercising them. Just remember that the 12 month CGT clock resets when you exercise options as they are considered a separate instrument.