If you consider the path from PPL to CPL, as part of your hour building you could easily do 50 hrs XC PIC, then do the SE IR gaining a further 30 hrs, then do the night rating and be at 155 hrs ready to commence the CPL, saving yourself 30 hours worth of hour building.
Not sure that your plan will work.
FCL.610 IR(H) – Prerequisites, experience and crediting
Applicants for an IR shall:
(a) hold:
(1) at least a PPL(H), and:
(i) the privileges to fly at night in accordance with FCL.810 i; or
(ii) an ATPL in another category of aircraft; or
(2) a CPL(H).
And from CAP 804 Section 4 Part L Appendix 6
B IR(H) — Modular flying training course
1 The aim of the IR(H) modular flying training course is to train pilots to the level of proficiency necessary to operate helicopters under IFR and in IMC.
2 An applicant for a modular IR(H) course shall be the holder of a PPL(H) with night rating, or a CPL(H) or an ATPL(H).
Also. I'm sure you are aware of the following with regard to the night rating:
FCL.810 Night rating
(a)
(b) Helicopters. If the privileges of a PPL for helicopters are to be exercised in VFR conditions at night, the applicant shall have:
(1) completed at least 100 hours of flight time as pilot in helicopters after the issue of the licence, including at least 60 hours as PIC on helicopters and 20 hours of cross-country flight;