What type of 90 day visa did you receive ? I am only familiar with the Non O 90 days for visiting family or retirement. Otherwise, just the normal 60 day visa.
If you do indeed have a 90 day visa then the dates of the visa of 13Sep2024 to 11Dec2024 is the visa validity dates; as long as you enter between those dates, you will receive a 90 day stamp.
just a reminder that while certain "short cuts" may be common, an agent falsifying financial requirement is illegal. People can do as they wish but should be aware.