Yes, Varshitap can be started tomorrow if you are physically and mentally prepared and you take the proper sankalp with discipline.

In Jain Dharma, the main points are:

• start with pure intention
• follow the rules of upvas and parana according to your tradition
• keep ahimsa, samayik, pratikraman, and restraint strong
• ideally begin with guru’s guidance or according to your local Jain tradition

If you mean tomorrow, 21 April 2026, it is fine to begin then provided your vow is taken correctly and you are ready to observe it faithfully.

For a vrat like Varshitap, discipline and sincerity are more important than merely the date.