6 days are enough for both the places. You can visit snow mountains and do river rafting, river crossing, paragliding & zorbing in Manali.
To cover Kullu Manali, it is recommended to plan a trip of at least 5 to 7 days. This duration allows you to explore the scenic beauty, visit attractions like Rohtang Pass and Solang Valley, engage in adventure activities, and experience the local culture and cuisine.