Low mass stars take a long time to proceed from the protostar stage to the main sequence stage, so in only 3 million years they would not have reached the main sequence yet. Suppose a new 1-M sun star began forming about 10 pc from the Sun. However, in the infrared, through a telescope, as the protostar began to form from the molecular cloud, we would see the star brighten and shrink in size. The star continues to gradually shrink, becomes dimmer, and in several million years it enters the main sequence. A star with large amounts of hydrogen will have a longer period of stability.
Instability occurs when a star runs out of hydrogen to burn, and then evolves off the main sequence.