honeymoon period

Short definition from Wiktionary

Noun

1. 1
   A relatively brief period when a new leader is given greater leeway with respect to changes he or she wishes to make.
2. 2
   A relatively brief period when a new loan has a low introductory interest rate that features prominently in advertising.
3. 3
   The length of time at the start of something new, particularly a new job, in which mistakes may be overlooked.
4. 4
   The early part of an intimate relationship, during which the couple are infatuated with each other.