What is the normal timescale in finding a breast cancer and being operated on? In relation to 5mm of intraductal carcinoma grade 3?

Varies. This can depend on your overall health, your surgical risks, timing of getting a surgeon consultation. Availability of the operating room, scheduling with radiology to localize such a small lesion of 5 mm. Etc. This may take 1-3 weeks to schedule depending on these and other potential factors.
6-8 wks. Intraductal cancer is not invasive. Grade 3 is more aggressive. If diagnosed via core needle biopsy, important to know that there may be invasive cancer present. This type of cancer will likely evolve into invasive cancer over time. Take your time to make a well informed decision. Maybe get a second opinion. Nothing will change over that time frame, and you'll be happy w your decision.
Month. I tell my patients that once you decide to operate you should do it within one month time.