
The benefit will be taxed as ordinary income and will occur when the option can be exercised at the vesting date and at the date of exercise.
If there is a possibility for you to choose between obtaining a share or payment in cash then the taxation will occur when you actually exercise the option regardless if you chose payment in cash or shares.
If the employer decides whether you shall receive shares or a cash payment when you exercise you SAR, the taxation takes place when the option can be exercised at the vesting date and at the date of exercise.