Generally speed development works by first building speed then extending distance. In the sprint world you can hear all about short-to-long vs long-to-short but that's usually framed within the context of the overall plan working toward a competition, not specifically with the order or periodization of top speed specifically.
With distance runners hills are a good starting point since they train maximally, but at slightly slower speeds making them a little safer and easier to control. The positioning and mechanics also mimic a lot of what we see in acceleration work so the translation makes sense; you're basically working on the first 30-40m when you do hill sprints. The 60m that you're doing is totally fine.
From there we want to see the athletes achieving higher speeds. This can be done by either lowering the grade of hill or by making the sprint on the flat. You'll usually start our around 40 for most of these and keep the recovery fairly consistent with what you were doing on hills initially. As you go recoveries can be extended to make times even faster. Generally for 40m we'd use 1:30-3:00 as a recovery depending on where we are in development and what the goals of the workout are. We keep it to 40m early on because it's working a similar area of acceleration that hills did, but in a different way (flat and with more velocity).
After that we transition into speed development which for simplicity sake is longer than 40m, but not so long that you see any slowing down. 50-60m is a good wheelhouse to be in most of the time. I used to go out to 80m for these, but after getting a FreeLap system I noticed that even distance runners rarely see their fastest 10m split after 50m (despite so many saying they hit top speed later).
After that point you've built top speed and need to work on extension, this is where speed-endurance comes in. 80-150m is usually what I think of with this. We typically go through a period of mixing a few shorter sprints with a few longer ones (ex/ 4x50m + 2x120m) so we can keep building speed and make sure that they know we want the same feel on the 120's as we had on the 50's. These should have much longer recovery 4:00 minimum.
After this point we've likely developed things as far as we need for most distance athletes. Going longer is still very useful, but a slightly different workout that could have been going along side these the whole time. That said I do think it's helpful to have the occasional workout that just asks for 3x200m or 300m + 100m, things that blend speed and glycolytic demand.
You can always revisit a hill workout for a change up or even try downhill running, just be careful with it and understand that it's a significantly greater demand, especially on the hamstrings.
Most of these workouts are pretty easy to do weekly or in the 3-4 times a month range. I put them the day before workouts where a lot of coaches might put in strides. 40-60m should be your bread and butter. I'd even place cones in the last 10m to specifically trigger you to think, "I need to be running as fast as possible here," to make sure you're focusing on the top speed aspect . Sprinting, true sprinting, is so foreign to most distance runners that even the basics done for years on end is enough. Don't get too hung up on periodization