Wait, you said you advanced some days? I hardly consider "a few days" to be a few months. So I'm assuming you meant January 4th instead of July 4th and you just made a typo mistake.
I think the game does production and such every 5 days. The reason it says something like "January 2 2025" instead of the actual date of it's completion is because, if the game actually calculated production each day it would be that exact date. But in truth it doesn't, it calculates every 5 days after the last calculation instead. So every time you reach that supposed date it pushes it up again and again until it reaches a date that's 5 or more days after the last calculation. So, for example, I have four missiles that are due in 3 days. The game won't calculate the building until it reaches a 5 day increment. So If my missiles were supposedly going to be completed at January 23, they would actually be built at January 25. And if I advance one day at the time, the game will compensate for me being in that date by pushing the supposed completion date up by one day, and will continue until the needed increment. So If I advance from 20 to 23, it would bump up the finishing date to 24. If I continued to 24, it would bump up to 25. If I advance to 25, the game would calculate the construction, and thus the missiles would finally be built. But as I said the calculation date is 5 days after the last calculation. (Note: After this point all this is speculated, I've got no proof, but I don't see any other explanations) The normal even 5 day calculation can be moved by interrupts. So, for example, if one of my 30 day increments were interrupted down to 8 days, the game would calculate a 5 day increment and the average date of calculation would be moved upwards by 3 days.
Anyway, all you have to do is advance one more day until it's July January 5th and your missiles should be built.
I think the way to change the calculation increments is by the "Construction Cycle Time" option. By setting it lower to, like, 80000, it would possibly calculate every day. I'm not sure though because I never tried it myself. The problem with doing this is that each one day increment could possibly take as long to process as a 5 day increment. But then again, I'm not sure because I've never tried it myself.