Uncooperative RP or unrealistic time scale? Sometimes it's matter or perspective.
When I was an IO, my team were sympathetic and tried to be reasonable, but had very little understanding of the commercial or procedural difficulties involved with complying with some of the larger changes that may form part of an enforcement notice. For example, 3 months to carry out significant work to a fire alarm system may seem more than reasonable to many IOs who have little or no experience in procurement matters. For public authorities, such procedures can take much longer. And with private companies (especially SMEs) there's no point causing extreme financial hardship.
I was a huge advocate of extending the time given - perhaps several times- if the RP could demonstrate he was making reasonable progress. Plus, what fire service would want to risk a potentially expensive prosecution if, with some patience, the notice will be complied with just by some gentle nudging by the IO?