What year do immigration in America count from example F4 priority for sibling to join USA as I’m a citizen of the USA?

After you file your petition for your sister's immigration, that application must be approved for further processing upon proof of your legitimate relationship to your sister. IF the petition is accepted for processing, it is given a Priority Date. When your Priority Date becomes current, your sister will receive appointments for visa interview, biometrics, etc. 

Currently, it has been taking 13-15 years for Priority Dates to become current for Indian-citizen siblings of US-citizens. So if you file your petition in 2021, you'd probably get a Priority Date around 2022, and maybe she will get an interview for an immigration visa around 2036-37. That's based on current rates of visa issuance, but there are so many Indians trying to bring in relatives, it is far more likely to take a lot longer than currently - and that's IF US continues to allow sibling-sponsorship (there's been consideration of abolishing that & limiting immigration sponsorship to spouse, child, perhaps parents only). Of course, you must continue to meet earnings requirements for the Affidavit of Support, and those requirements increase annually due to inflation. 

"The date is assigned once the USCIS approves of the immigration petition." That usually means when they receive a valid petition. 

https://www.uscisguide.com/information/priority-da...

The State Dpartment is currently processing F4 petitions filed in 2005:

https://travel.state.gov/content/travel/en/legal/v...