The theme of time is inextricably bound to Hal's educational process. Shakespeare felt free to rearrange time to suit his own ends. For instance, he made Hal and Hotspur the same age to better contrast their approach to time. Historically Hal was a baby when Hotspur was already battling the Scots. He looks forward to his future kingship at the same time that he looks backward to the deposed Richard II's squandering of time.
Time brings disillusionment, decay and death.
The chimes Falstaff and the dotty Master Shallow heard at midnight happened a long time ago and many of their friends are dead. Falstaff is losing his battle against time. He can evade it, but not escape it. But time also brings hope, renewal and redemption. The dying generation is replaced by a new order led by the heroic Henry V. England is healthy once more.