It matters if you are asking will you be required to give evidence. If you did not witness a crime but only provided information which encouraged the police to launch an investigation it is unlikely your evidence will be needed.
However, if it is needed, your bad character could be raised in court, though it is unlikely. As far as the Rehabilitation of Offenders Act goes there are minor differences in its operation in Northern Ireland but I do not know hat the differences are. In England and Wales the rehabilitation period for a prison sentence of less than six months is indeed seven years (three and a half years for those under 18) and it begins from the date of conviction regardless of the fact that the sentence was suspended.