I'd not recommend taking a trip that long right before interview. First reason is you may miss the FP or Interview notice, and the second (more important) reason is the IO might get the impression you have moved abroad and are just visiting the US for the interview.
A better solution is to wait until you have been through the process, got your USC then you can travel for as long as you want. If you break continuous residence beforehand, you are throwing away 5 years of long waiting.
