The heaviest downpours will occur between 12AM and 9AM with it scattering more (but still heavy) until Noon. Past that scattered showers/storms still possible but on a much lower scale.
Flood watches extend over the area for:
Southern half of CT: Sunday 2AM-eve
NYC: tonight 10PM-Sunday eve
NJ: tonight 8PM-Sunday eve
LI: tonight 11PM-Sunday eve
Beware of localized flash flooding occurring, especially at night when it's less visible when you're driving. Stay home if you can but be very careful if you need to go out and keep a keen eye out as visibility will be near zero during the downpours.