Deadline for Determination Letter Application for Initial Qualification

Is there a specific deadline for requesting a determination letter for the initial qualification of a new individually designed plan?

The instructions to Form 5300 do not appear to contain a deadline, nor does Rev. Proc. 2022-4. By contrast, there are specific deadlines for determination applications for merged plans.

There is not a deadline/due date. If an IDP has never received a D-letter then it is eligible to apply for one at any time. However, submitting within a certain time after a new plan is adopted can afford the sponsor a remedial amendment period to correct any deficiencies without penalty. If a plan waits 3, 4, or 5 years, for example, and then submits and there is a deficiency beyond the applicable provision's RAP (or whatever the current terminology), then I think you're looking at audit CAP.

And if the plan was first in existence no earlier than January 1 of the 10th calendar year preceding the year in which the application is filed, you may be exempt from paying a user fee if you meet the eligible employer requirements under Exemption From User Fee in the instructions to the Form 8717.