The rules behind the dates
A VLS-TS must be validated online on the ANEF portal within 3 months of the date you entered France: the date on your entry stamp, not your lease, your address registration or the date printed on the visa. Count it as a calendar date. Leaving and re-entering France in that window does not reset it. Miss it and you are no longer legally present, even though the sticker still looks valid.
A visa marked “carte de séjour à solliciter” has no online validation. It is stamped with a deadline of 2 months to apply to your prefecture for the residence card.
The first renewal is requested online between the 120th and the 60th day before your permit expires (CESEDA article R.431-5), roughly four to two months ahead.
When a month is shorter than the one you arrived in, the calculator gives the earlier day (arrive on November 30, validate by February 28). This is information from official sources, not legal advice; your prefecture and the ANEF portal have the last word on your case.
Read the full guides: Validating your visa after arrival · VLS-TS or carte de séjour à solliciter?