How do you imitate days passing by when writing a book?

Add an action sentence to the transition, i.e.

After waiting patiently a week Robert found himself rushing into the emergency room...

It wasn't until Sunday that Jenna finally left the gloom of her grief...

A month was all Nick needed to prepare for the hit on the Governor that morning...

Write a scene that describes them setting up camp. Include subtle statements about the wear on the equipment, the practiced ease of their team work, and the dwindling supplies.

Or simply describe a change of seasons, a hair cut, the growth of a scruffy beard, the finish of a project requiring many hours work or some such. For that matter, not having seen someone for along time is the perfect idle chit chat. Have your charcters actually act like real human and discuss their recent lives, rather than like stage actors who only talk of Chekov's gun.