You need to have 8 hours of fasting ideally for accurate measurement of fasting blood sugar. For post prandial samples..a gap of 2 hours is required after meal. HbA1C test can be done with fasting sample. But a word of caution while interpreting these test results and jumping to a diagnosis. There are various factors which may lead on false high or low HbA1C so a detailed history may help in reaching to a diagnosis.