I liked when Dancing lights was bonus action ...
I know it should not, but i liked it ...
Anyway, it seem to me like it have halved duration ... maybe even less. :-/
I dunno if that was only bug, or not ... but when i casted dancing lights, it was gone it two or three turns. :-/ Yet if im not wrong, it should work forewer, resp. as long as you keep concentration.
https://roll20.net/compendium/dnd5e/Dancing%20Lights#content