I have found things like this to be much easier with automations or checkboxes like you said. Pipelines date/time is screwy as heck and not something I have had great luck with. It isn't 1:1 with how automations worked with date/time in my experience.
I had one automation that got converted over to a Pipeline that was so simple. All it did was look to see if a date was on or before 5 days in the past. The conversion tool screwed everything up and I had to manually fix it. Which ended up causing like ~50 records the automation had missed over the last few years to suddenly spring into action and do things lol. After that, it worked as expected.
I think your code may work just fine if you do - instead of +. Give it a try and let us know.
