Review the agenda in detail and ask if there are any late items or walk-ons. Get to the first item on time. Introduce each item on the agenda and work a smooth transition between items. As the host, be thinking of a first question yourself, just in case. Keeping a meeting on schedule is a delicate balancing act that takes skill and luck.
Meetings tend to run long.
After introducing each segment, look at where you are in the agenda, pay attention to the speaker, watch the door nervously for the next speaker to arrive, all the while looking charming and pleasant. You can do it. If you need help, deputize a person to help you watch the time, with them signaling you and the speaker. Anything more can be distracting. If the speaker is using visual aids, you can generally see progress through the talk by watching the slides move around the carrousel or the overhead transparency stack get shorter.