I recently had a game of Fortnite on my laptop. The evening before, it definitely took 2 hours before the game ran reasonably smoothly. The next day I gambled a little at noon. At this point the game ran smoothly after the second round. The following evening it took forever again. What is this difference in performance related to? Maybe the internet connection?
Bad Internet.
May depend on how "clogged" the server is or how the bandwidth is distributed regionally.
It also depends on whether you have FPS drops or a high ping.
Do you generally mean the performance from the computer or the lag from the Internet?
Internet can cause problems in the evenings because several people use it. It also depends on the provider and location.
If the performance of the PC itself is different, I would guess a temperature problem, but actually it is not really called outside at the moment.