Start the blood test today. By next cherry blossom season, you and your best friend could be sniffing the sakura in Ueno Park.
Crucially, you must wait 180 days after the second vaccination blood test (sent to a designated lab) before you enter Japan. If you do this correctly, your dog enters directly with no quarantine. If you mess up the paperwork, your dog faces up to 180 days in a government检疫所 (quarantine station).