Just shorten the intervals. It's not a big deal. When I did yoga training in the pramayama (breath work) they started with quite short intervals, and the retention without air in the lungs was skipped at first.

It's completely fine imo and I don't think there's a need to get hung up on details like hitting a prescribed 4-4-4-4. 3-3-0-3 would be ok too.