Filter observations on timestamp
Filter observations on timestamp

fixes #93

newmanw/mage-server,newmanw/mage-server,newmanw/mage-server,jclark118/mage-server,ngageoint/mage-server,ngageoint/mage-server,ngageoint/mage-server,jclark118/mage-server,ngageoint/mage-server,jclark118/mage-server