Added option to start exam which serves as an alternative to start date for the exam

src/dashboards/Student.tsx

@@ -174,14 +174,14 @@ export default function StudentDashboard({user}: Props) {
 												className="tooltip flex h-full w-full items-center justify-end pl-8 md:hidden"
 												data-tip="Your screen size is too small to perform an assignment">
 												<Button
-													disabled={moment(assignment.startDate).isAfter(moment())}
+													disabled={!assignment.start}
 													className="h-full w-full !rounded-xl"
 													variant="outline">
 													Start
 												</Button>
 											</div>
 											<Button
-												disabled={moment(assignment.startDate).isAfter(moment())}
+												disabled={!assignment.start}
 												className="-md:hidden h-full w-full max-w-[50%] !rounded-xl"
 												onClick={() => startAssignment(assignment)}
 												variant="outline">