As KevinF said: times at the Seagull can vary depending on weather conditions, fitness, and a host of other variables. Simply enjoying the ride is key.
A great training route for the Seagull is any of the "Three Sheetz" (100 mile) or "Short Sheetz" (50-65 mile) variants led by Potomac Pedalers out of Frederick (take a look at the ride schedule to see what's happening as far as organized rides are concerned with the Pedalers). These are rural, mostly flat-to-rolling century routes that are ideal prep.
Also worth looking at is the Bay Country Century out of Owings, MD (map of route here), which is also flat-to-rolling and quite scenic, taking place on Labor Day Weekend.
And to toot the Potomac Pedalers' horn one more time (full disclosure: I'm the current chair of said club), the Back Roads Century is another good prep ride for the Seagull. It's more rolling than a Sheetz route or the Bay Country Century, but it's not overly hilly and is very scenic. Like the others, there are shorter routes, and there will be plenty of people to ride with to get you back in the mindset of riding in a group. The Back Roads Century is filling up fast (less than 250 slots left), so enter soon if you want to ride it.