A lot of my flash fiction stories are set within a very short time period (appropriately) and are written in the first person, precisely because I want to achieve a sense of "immediacy". For other pieces I have the lead character looking back at their lives and being reflective so the time within stories like that is longer, "stretched" if you like, and the pace of the story is slower. What grabs you with those kinds of tale is the character - something about them intrigues you enough to make you want to find out more.
Time in itself can make a useful theme for stories (too little of it, too much of it etc) but I've found it helpful to think about the kind of story I want to tell and then work out what the best time frame for that tale would be. In my Pressing the Flesh the opening line is "It was 3 am". The impact of that is to make you wonder (a) why the time is important and (b) to assume the character concerned is unlikely to be up to any good at that time of night. (Quite right too - see my From Light to Dark and Back Again for the whole story!).