You are correct in thinking that you need 500hrs and it is total time. You also need 30 hourse PIC in a MEP(L) aeroplane of which 10 hours must have been in the 12 months prior to applying for the rating.
JAR-FCL 1.380 - CRI(SPA) - Requirements
Date: June 1, 2000
(See Appendix 1 to JAR-FCL 1.330 and 1.345)
(See AMC FCL 1.380)
(a) Multi-engine aeroplanes. An applicant for the issue of a CRI(SPA) rating for multi-engine aeroplanes shall have:
(1) completed at least 500 hours flight time as a pilot of aeroplanes;
[(2) completed at least 30 hours as PIC on the applicable type or class of aeroplane of which at least 10 hours shall be in the last 12 months;]
(3) completed an approved course at [an approved FTO or TRTO including at] least five hours flight instruction on the aeroplane or a flight simulator given by an instructor approved for this purpose (see AMC FCL 1.380); and
(4) passed a skill test in accordance with Sections 2, 3, 5 and 7 of Appendices 1 and 2 to JAR-FCL 1.330 & 1.345.