You have three years to attain an EASA professional licence from the date of last exam pass. It does not matter whether it's an ATPL or a CPL, so multi crew hours do not matter here - at this stage.
An ICAO IR (current) will keep the ATPL theory credits valid for seven years, after issue of the EASA licence.
500 hours on a certified multi crew aircraft will exempt you from the MCC course. Certain proviso's exist for single pilot aircraft operated multi crew.
Section 4, part A, Paragraph 3 of CAP 804:
(c) Validity period
(1) The successful completion of the theoretical knowledge examinations will
be valid:
(i) for the issue of a light aircraft pilot licence, a private pilot licence, a
sailplane pilot licence or a balloon pilot licence, for a period of 24
months;
(ii) for the issue of a commercial pilot licence or instrument rating (IR), for
a period of 36 months;
(iii) the periods in (i) and (ii) shall be counted from the day when the pilot
successfully completes the theoretical knowledge examination, in
accordance with (b)(2).
(2) The completion of the airline transport pilot licence (ATPL) theoretical
knowledge examinations will remain valid for the issue of an ATPL for a
period of 7 years from the last validity date of:
(i) an IR entered in the licence; or
(ii) in the case of helicopters, a helicopter’s type rating entered in that
licence.
Last edited by Hawker 800; 6th May 2016 at 10:48.