Hey Keliptic,
Thanks for writing in!
Based on the screenshot alone here - it's tough to speculate as to what exactly your issue here may be. With your description, and what we can see in the image - it *seems* like you're headed down the right path, but we'd recommend gathering some more information to be certain.
If you think it's a time based problem (happening between 5-10pm), then you'd ideally want to trace continually for at *least* 24 hours (but 48 hours would help to paint a better picture of the problem). Your goal is to show problem periods, as well as good periods - so that you can correlate any patterns that occur in your results with poor network performance. This helps you not only narrow down the issue - but helps create a stronger case if you should happen to need to take these results to your ISP.
We've got a guide that goes over some best practices for troubleshooting an issue like this, which you may find useful here:
http://www.pingplotter.com/netnirvana/If you should find yourself with any other questions, or needing any guidance - we're always happy to try and help out as well! Feel free to send over any .pp2 files you'd like, and we'd love to take a look and offer any guidance we can.
Best wishes,
-Gary