don't worry. i was on the list - and lucky me - never got 抽中. i was surmon to be juror list every 2 years but none got selected.
you could attach your surmon letter with the vacation leave application to HR. they could not deduct from your payroll, but that serve the record. in case you got selected, the company will have to grant you the pay leave.
and if they did not want you to be selected, they will have to back you up for whatever reason you provided.
one of our colleague , had request the company to issue the letter saying he is stationed in china. so can't stay in HK for so long to be the juror.. (but in fact, he is just the frequent traveller).