My experience is that it will wait till you press enter and then a msg is sent from the node.
But if you then tab out of the field, two instances of the msg are send. Here is a flow (ui_text_input => debug) with the issue:
[{"id":"a742f7f6.d6fa68","type":"ui_text_input","z":"400c8386.3b0104","name":"","label":"delay 0","tooltip":"","group":"dcf2fce6.0eb518","order":4,"width":0,"height":0,"passthru":true,"mode":"text","delay":"0","topic":"","x":440,"y":100,"wires":[["37645fdd.8d364"]]},{"id":"37645fdd.8d364","type":"debug","z":"400c8386.3b0104","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","x":630,"y":100,"wires":[]},{"id":"dcf2fce6.0eb518","type":"ui_group","z":"","name":"Default","tab":"df3f2d27.786758","disp":true,"width":"6","collapse":false},{"id":"df3f2d27.786758","type":"ui_tab","z":"","name":"Home","icon":"dashboard","order":3,"disabled":false,"hidden":false}]