I am writing a short story, and I have some gaps in time I have to fill. In my story, a girl wants to go to a party later in the day, but there are a few hours in between the events. What could I put into the story so that I'm not just skipping through time?
Skipping through time is totally legitimate, and often the best choice.
You can just leap there:
"At 7:15--her mother's advice regarding the precise definition of "fashionably late"--she knocked on the door."
You can summarize the time:
"The rest of the day was filled with preparation, from an appointment with her mother's hairdresser to a near-tantrum at Macy's when the skirt that she had been eyeing for six weeks was suddenly sold out. But finally, at 7:15--her mother's...."
Or you could take an event from elsewhere in the story and insert it in the day, if that seems to work.
If it's not developing characters, or setting up a plot via foreshadowing or simple detail establishment, if there's nothing of interest to note and you yourself, the writer, think it's filler, don't include it.
Time skipping is better than time wasting
You can use the time to point up how bored and/or nervous your protagonist is, but really you're torturing yourself writing boredom in detail and you're really torturing your readers by expecting them to read it. Skipping a large chunk of time and still showing the reader that it was torturous for the protagonist is simple:
"Something, something, not important.
'* * *'
"Six excruciatingly dull hours later [your character here] couldn't wait any longer..."
Or you can do some detail work about her preparations but again with the torturing thing.
Why would you want to fill the gap? Either you have something interesting to say or you don't. But don't write something just for the sake of writting someting, it will be boring.
If you are looking for transition, just write something like: "The time to go to the party had arrived, ..." or "Five hours later, ...".
If you want to show that the time is passing slowly for the character, you can say that and then describe the attempts that the girl make it pass faster. I would recommand something like:
3h before the party, Girl decided to empty the trash.
2h55 before the party, the trash is empty, Girl decide to clean her room.
2h30 before the party, the room is clean. Girl is bored.
2h20 before the party, Girl notice a fly is buzzing around.