BRUSSELS (Reuters) - The Eurogroup of euro zone finance ministers will meet at 2 p.m. (1200 GMT) on Saturday, bringing forward by three hours a vital meeting to discuss the Greek debt crisis, a spokesman for its chairman said on Friday. "Tomorrow Eurogroup starts at 1400 instead of 1700 at the request of Eurogroup members," tweeted Michel Reijns, a spokesman for Eurogroup President Jeroen Dijsselbloem. (Reporting by Alastair Macdonald; @macdonaldrtr; editing by Philip Blenkinsop)