Sometimes, players don't complete tasks during the timed phase in a timely manner. Aside from confusion, is there any game-enforced consequence?

Well, the Communications officer should me monitoring the time remaining and announcing when it runs out. When it has, you don't get to continue that action - you're stuck with whatever you have on the board.

So, for example, if you're on the fence about how many interceptors you can afford to deploy, and don't deploy any - tough.

I think it also eats into your Pause time too and possibly scrambles the Timed Phase ordering too. Basically don't go over - if you must then use the Menu pause feature but only if you're explaining rules or the such like to newer players.

The game would get very easy too quickly if you take extra time to work out the best strategy - it's supposed to be a pressure decision game.

I don't think it's practical to enforce that incomplete actions should remain so. I haven't noticed less pause time.

I was hoping that there was a demonstrable consequence like additional saucers. Will a designer respond?

You might not think it practical, but that is the ENTIRE POINT of the timed phase being timed.

As for reduced pause time; that's something which only applies during Normal or higher difficulties. Clicking 'done' before the timer turns red will bank you more pause time this round. Unused pause time gets put into a pool at the end for additional 'timed phase' abilities to be used.

Furthermore, running out of time on an action gives you even LESS time for the next action. If the consequence for running out of time wasn't leaving actions unfinished, why would they penalise you in this fashion?

And if the penalty was ANYTHING ELSE (such as spawning more UFOs as you suggest) don't you think that would be mentioned somewhere in the tutorial?

From the game overview in the tutorial:

During the timed phase, the app provides players with different actions to perform. Players will have a finite amount of time to perform these actions before the next action appears.

From the section titled 'communication interface':

B) The Timer. This indicates how much time players have to perform the current action.

*snip*

D) The "Pause" Button. You can tap this button to pause the timer if a player needs more time to complete the current action.

Since it's a cooperative game, there's no motivation to enforce incompleteness, so if they carried on, it would just happen. I haven't noticed whether less time is allowed following an incomplete (and I'm not sure how that could be determined), but it seems like a relevant penalty.

What's the motivation to play ANY co-op according to the rules? To beat the game fairly. If you house rule things to make the game easier for yourselves that's fine, just be aware that you're no longer playing the game as intended.

Perhaps I wasn't so clear above, but if you're not sticking to the time limits to perform your actions, then having less time within which to perform your action isn't a penalty at all.

Since it's a cooperative game, there's no motivation to enforce incompleteness

You mean apart from the fact that you won by cheating?

For blue/yellow (XCOM) actions, when the time runs out, that's it. If you haven't done them, tough luck, you've missed your window of opportunity (I'd be inclined to make an exception for the budget).

For red (alien) actions, when the time runs out, you lose half the time for the next action, and it starts eating away at your pause time. You can't continue with the game until the action is completed. Aside from choosing the lesser of two crises, there's no choice involved in alien actions, so there's no reason they should be at risk of overrunning on time...

That's more of a penalty than is enforced for not placing UFOs when told to, for not increasing panic, for rigging the dice rolls, or for lying to the app at any point...