The two week delay simply reflects the length of time it takes (up to 10 working days, actually) to process the pay actions once they've been input in the pay system by the unit OR. The pay actions put in the system are checked by the system for accuracy, validated, the necessary deductions are calculated and made and then the etransfer "tape" is cut for transfer to your bank account. All this is done on a batch basis rather than individual transactions - i.e. the transactions are accumulated in a batch. To ensure that this batch processing is done consistently, there is a cut-off date for each pay period - once that cut-off date is reached, all transactions in the batch are processed. Actions put in the system after the cut-off date for a pay date will be reflected on the following pay. The RegF and Civil Service pay is managed the same way. Since we're paid on the 15th and the last day of each month, pay for days worked in the two week period immediately before a pay date will be reflected in the following pay date.
The pay system for reservists actually works nowadays, compared to a few years ago when it could take much longer for your pay to be processed (if it was at all).