Hey Pranav Yess these places can be covered in time of 4 days but it ll be a bit bhaagam-bhaag at times.
I would suggest you to include two places for one trip the other one you can try some other time , so that you can explore those two places fully . remember yeah Jawani hai deewani dailogue 'itna mat bhaag bunny ki zindagi peeche chut jaaye , Jahan ho vahi k maze lo ' 😂
anyways according to me go for Rishikesh and either of the two places (by your choice)
2 days for Rishikesh 1 n half day for second place rest for traveling.
in Rishikesh :
Day 1: go for river rafting and local sight seeing(ramjhula , Laxman jhula , local market and cafes , mandir ) also you can go to Patna waterfalls (must visit ) should go there in early hours because after 10 it gets crowded. Day 2: go to Neelkanth and jhilmil gufa and some other caves 1 km ahead of the temple (best for adventure seekers) you can also go for bungee jumping flying fox nd other adventure activities if your budget permits or you can simply enjoy urself lying on the beaches. Then you can do a night traveling to Rudraprayag or you can travel In morning (5-6 hrs )
then explore rudraprayag in remaining time you can also go to Deoria tal lake trek which is 50 KMS away from rudraprayag
PROTIPS ( as you said)
1 : stay in dharamshala's or hostels 2: eat at local restaurants or shacks
3 : use public transport HAPPY TRAVELLING BUDDY
Yes it takes 3-4 hours to reach rudraprayag and Devprayags in between you could easily complete it within 4 days even if yiu get lagged by landslide and rockfall cause it's usual there , it would only cost around 2000 for 4 days if you're not alone