You can go to Tilos from Mandraki Harbour in Rhodes Town on the Sea Star catamaran, but from Lardos you would probably have to spend one night in Rhodes Town in order to catch the boat. http://www.tilostravel.co.uk/html/flights.html This shows the 2005 timetable, so you would need to check with Tilos Travelby phone when you get to Rhodes (David is English and Manos is fluent too!). Now for an honest opinion - I love Tilos, it is a little bit of paradise (I spent the seummer there a few years ago), but I think that if yoou just want a DAY trip, you might be better going to Symi as this is more immediately attractive. My suggestion would be to go overnight to Tilos and try and have a walk round the mountains!

Have a look at my pics here http://members.virtualtourist.com/m/7445b/65c79/