PvP Flag Broker
PvP Flag Broker (PFB) is a LibDataBroker addon that provides a customizable display of PvP flag information, including the time until your PvP flag "drops."
With WoW 3.0, Blizzard provided a built-in PvP timer to players. However, PFB provides customizability that the standard timer does not approach, including the ability to display the minutes and seconds remaining at all times instead of only the minutes remaining when more than 59 seconds remain... and of course its ability to be placed on the screen wherever your LDB display addon allows. (PFB can of course hide the built-in timer, and does so by default.)
Note: Older PvP-flag timer addons that I once counted as invaluable are not as reliable as PFB because they don't take advantage of functionality added to the game relatively recently that lets players know with certainty when their PvP flag will drop. Its display is also more customizable than that of those addons.