Fzyrrx:
I want to interface with a computer for data collection using USB hookup.
This is a vital part of your post. Since you are connected to PC, you don't need a RTC or an SD. If you use a proper terminal programme, like RealTerm, you can record direct to .csv file on PC's hard drive and timestamp the recordings using the PC's clock along the way. Further, you are just serial printing, which I understand is a lot faster than recording to SD.
You might also check the PLX-DAQ macro, which enables you to record direct to Excel, thereby enabling you to get live graphs.