Healthcare.gov year of college graduation sign up question

For a student classes ending April 29th 2026, graduating May 5th 2026, probably starting a job with insurance in June 2026:

I will not be claiming him as a tax dependent on my taxes because doing so would force me to add his income on the ACA form, which would then put us over the cliff and would be nearly catastrophic financially.

When I go to sign us up on the Healthcare.gov site, it only offers "dependent" and wants the income estimate.  Technically his job is still an offer and not secure.  I can leave it out of the estimate and file a change of circumstance with HC. Gov as soon as he shifts to the new insurance.  

Is this how this is handled or am I simply not allowed to have him on my plan even though he is my dependent as of Jan. 1st through June?