Pompei and Mt Vesuvius one day

You can see Mt Vesuvius from Pompeii.

For the time it takes to get there, hike to the top, and the short amount of time AT the top…
N O!

Is it possible to do both ? Yes, if you have a full day. I personally wouldn't cut Pompeii short to do it; but how short is short? We were there for 6 hours and didn't see everything we wanted to. Time of year is also a factor. I think anyone trying to hike Vesuvius on a summer afternoon would have to be out of their ever loving mind. But if it's really important to you, here is a blog with extensive information on Vesuvius hikes:

https://www.alongdustyroads.com/posts/hiking-mount-vesuvius

I took a early morning guided tour of Pompei, had lunch at the restaurant at the Circumvesuviana Pompei Scavi train stop, then took a bus to Mt. Vesuvius. I walked to the top, very steep, walked another 45 minutes around the crater, then had to turn around so I would not miss the last bus.

The Pompei tour took about 90 minutes. Was taken to the " must see" spots in Pompei. While I enjoyed Pompei, the next day I visited Herculaneum and LOVED it. Herculaneum is smaller, easier to view, fewer crowds, the guide was better, quality of sites were fantastic. Do not miss seeing Herculaneum!

The hike to get up Mt Vesuvius was exhausting, the views were great. I would have spent more time walking around the crater but had to leave to catch the last public bus to the train station.

Yes, you can do it but it will take a full day if you are using public transportation.

PS: Bring plenty of water and sunshade for hiking Mt. Vesuvius.

Is Mt Vesuvius worth cutting Pompeii a little short to see it?

If after 6 hrs at Pompeii you feel you have seen everything you want to see and still desire to go up the mountain, go ahead.

From your other post it looks like you have nothing planned for the next day, so you can use it to recover. Going in April will not have the brutal heat that going in summer would entail.