Program completion for immigration purposes is deemed to be the final day of the semester for students enrolled in a semester-long course which meets on regularly scheduled, specified days and times for the duration of the semester.   Students enrolled in condensed courses are deemed to have completed their programs on the last day of required attendance during their final semester.

GRADUATE STUDENTS WITH THESIS/PROJECT REQUIREMENTS

For those students who are enrolled only in graduate thesis or research credits and who have met all other course requirements in a previous semester, program completion is calculated from the date of thesis or project defense not the last day of the semester date.  The official program completion date for these students is either
(1) two months from the defense date or
(2) Thesis Requirement: the date the academic department chair signs the thesis/dissertation signature page or
Project Requirement: the date the project credits change of grade is submitted by the academic department chair,
whichever is earlier.

You can read the official policy memo here.