how long is the dipstick susposed to be

There is no measurement published for a dipstick. The best suggestion I could give is to perform a complete oil and filter change, add 4 1/2 quarts of oil as specified. Start and run the vehicle to circulate the oil, and then shut it off after a few minutes. Then insert the dipstick and measure the oil level. Where it measures will be the "full" line. If you need to cut it from then, you will be able to based on the accurate 4 1/2 quarts of oil in the crankcase and the full line after the fact.

It is supposed to be the same length as the original one was. Infiniti Part No.: 11140-10Y00 > $18.60