First week of August is the best time for this trek. It'll easily take 4days for a detailed and relaxed trip. If you're travelling somewhere far from Delhi, then It'll add on.
Itinerary would be:
Day 1- Reach Joshimath
Day 2- Reach Govindghat and then trek to Ghangaria (6hrs) then further to Valley of flowers (4hrs)
Day 3- Return to Govindghat n further to Haridwar.