The FAQs state end of April. But when we applied a few years ago -- we received the notification a week or so after their stated date (they said ed of April and we were notified in early May).
http://www.montgomeryschoolsmd.org/uploadedFiles/curriculum/specialprograms/admissions/Immersion%20FAQs13.14(1).pdf
You call always call to ask if they have an udpated date estimate: 301-592-2040
If you don't receive a notification before the Kindergarten orientation for your neighborhood school -- you should just have your child attend the orientation just in case.