"The stroke of five" means when the bell in the clock tower (ie. the local clock tower in the towns in the past) strikes at five o'clock. This is an exact time.

It means you aren't certain but that you think you will arrive by five o'clock. If you are certain , you would say 'I will be here at the stroke of five'.

Stroke, in this instance, means the sudden instant. The stroke of five means the very instant it is five o'clock. I should be here at the stroke of five means that I should be here exactly at 5:00. I hope this helps.

It mean that you shoul be somewhere at five o'clock. A stroke of five means a stroke of the clock at number 5.