What should be the theme of a presentation in a research visit?
Short answer: ask them to clarify; ask your PI.

To offer my own opinion, I would expect that for a research visit the appropriate contents of your presentation would be your latest research results. As you are visiting on behalf of your group, start with an overview of the group's main research areas and latest results (ask your colleagues to each make you a slide about their work). Then you could go into more detail about your own work later in the presentation. Perhaps pose some research questions that you think your two groups could work together on (take advice from your supervisor here).

If you get to set the time, a one hour slot with 45 mins + 15 for discussion will be plenty.