Night Flight
There's been much qouting of statistics, opinion and anecdotal reporting of accidents for night flight.
However, the actual statistics are that between 75-85% of accidents are related to pilot error. Of the remaining circa 20% it can be identified that the mechanical faults leading to the incident were, on too many occasions, apparent to the pilot before take-off (I don't know of any research that quantifies the percentage).
Whether flight by night or day it must be obvious that proper servicing, recording and identification of the aircraft faults including a thorough pre-flight inspection is paramount.
Flight by day or night requires carefull detailed pre-flight planning taking into account terrain, weather reports, icing levels and notified airspace. If this is not done then, day or night, you may enounter a problem irrespective of whatever rating you hold.
Multi engined flight brings with it its own problems owing to complexities; Handling characteristics following an engine failure, assymetric skills and of course the management of such things as fuel transfers which, particularly with some older types, can be complex. Add to that marginal in-flight conditions and strong gusts on approach with significant crosswinds and the two engine idea may not seem to simple a choice to make. The simplicty of one engine can at times be more attractive.
With regard to instrument skills it shouldn't be forgotten that instrument flight training was a requirement for the the Night Rating but was removed by JAA with the introduction of the Night Qualification.
To answer the original question. The 5 hours required for the Night Qualification may be included within the 45 hours minimum experience for the PPL but must be additional to the 25 hours dual/10 hours solo. If there is the opportunity to do it then it will be cost effective and increase the pilots level of safety that the skill and knowledge of flight at night adds.