2 - 3 Days - Lima
This would be my personal recommendation I know the opinions about Lima are very diverse. I did not have a lot of time to explore Lima, however what I see didn't really convince me of the beauty of the city. I think two to three days are enough to explore the main sights, however if you're planning to do a surf course which are broadly offered in the capital then you might need more days.
1 - 2 Days - Paracas
We just did the Paracas Natural Reserve (which is btw a free stop with Peru Hop) but if you also would like to see the Ballestas Islands. The Paracas Natural Reserve was one of my favourite stops, I never saw the desert meeting the ocean so it was a really nice experience.
1 - 2 Days - Huacachina
Due to my foot injury I was not able to do the main attractions in Huacachina which are Sandboarding and Dune Buggy. I really wished I could have done it because everyone said it is so much fun. I have never been to a town like Huacachina, which is a small village surrounded by dunes. You will have a great view walking through the city! I don't think you necessarily need to spend a night in Huacachina, however it might be more relaxing to spend the night there instead of staying only for a day.
0 - 2 Days - Nazca
This is also depending if you only want to see the Nazca Lines, if you are only wanting to see the Nazca Lines from the Tower then I would almost say to skip it because the tower is really, really small and you barely can't see anything. However if you're planning on doing the flight I would recommend 1-2 days, in case you would like to stay a night. You can also visit the city Nazca itself which has a couple attractions.
3 - 5 Days - Arequipa
We only stayed two days to leave us one day to explore the city and the second day to do a bus tour to the Colca Canyon. If I would have been able to walk (due to a foot injury I was my whole vacation not really able to walk long distance) I would have done the trek. The Colca Canyon is the second deepest Canyon, after the Grand Canyon. From what I have heard of the people I met is it a pretty exhausting trek but very rewarding! So if you have the chance to do it, do it! I will definitely do it the next time I'm in Peru..
2 - 4 Days - Puno
I would say one day is enough to explore the city Puno, but I would recommend a trip to the floating Islands which was one of my favourite things I did in Peru. It was really pretty, although you also kind of felt disrupting the daily life of the inhabitants. But on the other side I think the tourism also plays a big role in their life. We only did a 4h trip to the Islands, but you can also do a overnight stay to get to know the life of the inhabitants better!
2 - 3 Days - Cusco
Cusco, Puno and Arequipa were my favourite cities in Peru! I really liked Cusco there is a lot to see and you can do various tours! Again due to my foot injury I was not able to visit the Machu Picchu - which I think is a must see! So I have another reason to go back to Peru! ;-) Next to Machu Picchu you can also do a tour to the Sacred Valley or the Rainbow Mountain. So I would definitely plan a lot of time for Cusco!