First you want to avoid selecting a timing for your presentation that doesn’t suit (most of) your audience. But there are occasions where only when you are actually giving your presentation it appears that a number of the invited people were not able to attend. Considering that you had enough people and the presentation occurred, you now need to think about what to do for the persons who couldn’t attend.
Sending them an e-mail with the information may be an option, but that would raise the question why you had the presentation for the others who did attend. If only a few people didn’t attend it may be wise to offer a one-on-one personal session with them. During this session you can present what was discussed and allow them to answer question. When there are a number of persons who couldn’t attend you should consider to organize another session for them.