12. In computing the period of full-time volunteer service under regulation 10, no account shall be taken of —
any period before the day on which he reported for full-time volunteer service;
any period of absence from full-time volunteer service without leave or desertion where that person was convicted therefor;
any period, during which he was serving or would have been serving, if he was not unlawfully at large, a term of imprisonment, special detention, detention or reformative training; or
any period during which he was under close arrest or civil custody on a charge for an offence of which he was afterwards convicted by a subordinate military court or a civil court or by a disciplinary officer.