A notice of discontinuance occurs at the time the notice is served, not at the time it is filed, pursuant to CPLR 3217[a]. A discontinuance by stipulation occurs when the stipulation is filed with the court, pursuant to CPLR 3217[a][2]).
Bayview Loan Servicing, LLC v. Windsor, NY Slip Op 03560 (2d Dep't May 8, 2019)
Here is the decision.