Can I go braless for a few hours, five days after my breast augmentation?

Congratulations on having undergone the breast augmentation procedure; given that you have chosen your plastic surgeon, it is best to follow his/her "protocol" given that your plastic surgery knows what works best when it comes to achieving patient pleasing  outcomes in his/her practice.  
Generally speaking, there is no “standard” when it comes to the use of specific bras or garments after breast surgery. In other words, different plastic surgeons may have different practices when it comes to postoperative dressings/bras. 
In my practice, patients wake up with a surgical bra in place. This surgical bra, although not attractive, is supportive and used for about one month after surgery (some of my patients have been known to burn the bra ASAP). Then, patients transition to a soft sports bra. Wired bras are used when breast have reached their “final position” and patients have full sensation along the breast skin. 
Generally, the longer I have been in practice, the more I appreciate the long term use of supportive bras after all types of breast surgery.  This additional support may be especially helpful when patients are lying down and/or engaged in strenuous exercise. Best wishes for an outcome that you will be very pleased with.

This question is best answered by your surgeon as he/she knows what is planned for your surgery.  The use of support garments after surgery varies by surgeon as well as by patient based on the extent of surgery performed. Your surgeon will advise what is best for you.