Opening ceremonies are at 10 a.m. today at the Rockville station with speeches by officials. From 8 a.m. to 10 a.m., there will be free cider offered at Rockville and free coffee at Shady Grove. At both stations, there will be balloons, clowns and a Santa Claus. HOURS: The extension opens at 8 a.m. today. The rail system is open from 8 a.m. to midnight Saturday, 10 a.m. to 7 p.m. this Sunday (service normally stops at 6 p.m. on Sundays, but has been extended an hour on recent Sundays for Christmas shopping), and 6 a.m. to midnight weekdays. FREE RIDES: Free one-way rides from the four new stations from 8 a.m. to 4 p.m. today. PARKING: On Saturdays, Sundays and holidays, parking at Metro lots is free. On weekdays, parking will cost $1 a day at the White Flint, Twinbrook and Rockville lots; it will be free at Shady Grove for three months and then will cost $1 a day. RIDE-ON: Ride-On is offering free shuttle bus rides today from Germantown and Gaithersburg to the Shady Grove station every 15 minutes from 9 a.m. to 4 p.m. Shuttles will depart from Seneca Valley High School on Middlebrook Road and from the Gaithersburg commuter parking lot at Summit and Cedar avenues.