How to deal with presentation time running out in a scientific conference? I understand that it is not a good idea to speak more after your time is out during a conference presentation. So we generally distribute our total times among each slide depending the contents and priority during the preparation. But sometimes what happens one/two particular slides take little more time. As a results your time goes out before summarizing your presentation.

So I sometimes skip my summary and acknowledgement slides to avoid the loss of discussion time. I am wondering whether this is a good idea, or whether I should finish my talk with more 30–40 seconds?
First, some conferences have really strict timing and you will be given no extra time.
Second, if there is important slide or two, just do it. But make sure that you only slightly extend your time (e.g. 10%). If you are going to extend it by 50%, or 200% (I saw that, and I was pissed at both the speaker and even more - the chair for allowing that) - please, don't.
Side note: as a chair I am an ass. And while I give something like 1 min grace time (for 15 min talks), then after that:

speaker: &quot;But there is an important slide afterwards!&quot;
me: &quot;But not as important as other participants' time.&quot;

EDIT: By all means I recommend rehearsing and finishing on, or before, time. I only answer the question - whether to use extra 40 sec for 2 unfinished slides or not. &quot;You should prepare to avoid such situation&quot; is as on-topic as &quot;you should go fishing instead of attending a conference&quot;.
(If the question is &quot;Given X, should I do A or B?&quot; all legitimate answers should assume &quot;X&quot;, even if it is a suboptimal/nasty/unprofessional/embarrassing situation.)