In the first quotation, Amanda has just angrily told Tom to "go to the moon". Of course, she expects Tom to return as he usually did. However, her anger over the events of the evening and her subsequent accusations against Tom are the final straw. So, instead of "going to the moon" and returning, Tom simply abandons his family and never returns. Thus, time has separated Tom from Amanda and Laura in ways physical distance alone could not do.
The second quotation, however, indicates that in getting away from Amanda's bitterness, Tom also separated himself from Laura. Ironically, he did not see how attached to Laura he really was until he abandoned her. When he has been gone a long time, he realizes this attachment with the words, "I have been more faithful than I intended to be.
The last quotation is both a commentary on Laura's future and the condition of the world. During the scene with Jim, Laura had been literally and figuratively "lit" just like the candles in the candelabra. In fact, the candelabra is another symbol for Laura. It, too, had a "slight defect" having been burned in a previous fire. However, now that Jim is gone and Tom has abandoned the family, Laura has few prospects for a happy life. Thus, it is time for her to "blow out her candles". Tom's last observation is that Laura's candles are no match for the "lightening" and destruction of World War II which were to follow the 1930's when the play takes place.