Varshitap starts with Upvās (full fast).

In normal Śvetāmbara practice:

• Day 1 of Varshitap = Upvās (no food, only boiled water within the fixed time).
• Next day = Beshan / Byāsan (one or two meals, as guided by your guru).
• Then it continues alternate: Upvās – Beshan – Upvās – Beshan…

(with some special adjustments on important tithis like Chaudas, etc., as per your sangh’s calendar).

So, the tap itself is counted from the first Upvās day, not from an eating day.

For more detailed explanation of Varshitap you can read here