Countdown clock software

We run an event on an annual basis which acts as a corporate speed dating service. We require a piece of software that will run a sophisticated countdown clock throughout the date which would be projected throughout the event venue. This countdown clock will allow delegates to see how much time they have left of their current appointment before they must move onto the next appointment. The software must incorporate breaks throughout the day. An admin must also have the ability to speed up appointments in the event of a delayed start. Timings change for each event so the software must allow for different timings. An example itinerary for a half day event might be: 0900 to 0914 - Appointment 1 0914 to 0915 - Move to next appointment 0915 to 0929 - Appointment 2 0929 to 0930 - Move to next appointment 0930 to 0944 - Appointment 3 0944 to 1015 - Break 1015 to 1029 - Appointment 4... The projected image should simply have our branding around border and an egg countdown (rather than actual clock in event of delay). 'Move to next appointments' should simply be a countdown timer. Breaks should pause the program and await an admin to hit start before going to next appointment. We should also have the ability to upload sound files for each part. This might be a 'bing' for a 2 min warning, an announcement 'This appointment is now completed, please move to next appointment', and 'The appointment is now commencing'. Software needs to be able to run on a Windows 7 laptop and image resolution should be good enough for a very large projection screen.