Once the work to gather all safety case information (step 1) and analyse that information (step 2) has been completed, you can undertake the task of filling the gaps.
With Part 4 Section 84 of the Building Safety Act making it very clear that an accountable person for an occupied higher-risk building must promptly take all reasonable steps to prevent a building safety risk materialising, and to reduce the severity of any incident resulting from such a risk materialising, there is little wriggle room for whether these gaps must be filled or not.
However, with various funding challenges (including Section 20 of the Landlord and Tenant Act 1985) and leaseholders already fed up with the various service charge increases or one-off charges, the costs of filling the gaps should not be underestimated. In fact, making a provision now for an additional £40k-£60k for this very reason could be prudent.
Having the funds in place is one thing; having someone available to do the work is quite something else. The market has suffered from a lack of competent resources for several years; however, since the registration deadline on 1st October last year passed, demand has increased significantly, with lead times now over 6 weeks in many cases. And once the SCR requests start going out from the Building Safety Regulator in a little under 11 weeks (1st April 2024), there will certainly be another spike in demand.
This is all likely to take quite a toll on the principal accountable person, or more likely, the property manager taking care of all this on their behalf. In either case, delaying will only make things worse. Gathering the information, analysing the information, and making sure any gaps have been filled should be undertaken as soon as possible, as writing the safety case report itself is also not an easy task and cannot be undertaken without the right information.