Question 1: Which day's R1 should I use w/rt selling this position? What is the best way to approach this situation from a strategy based on pivot points?
Since an emotional response by traders at various pivot levels hinges on the current days pivot points (which are based on the previous days price action), it is advisable to execute orders at or near today's levels only. This assumes of course that you have some reason to believe that today's price action has an underlying impetus for reaching the level you have chosen as your target (R1 in this example). Realize that the existence of a PP does not in itself have any value with regard to price move prediction. Each day thousands of stocks trade without ever reaching any of their respective pivot points. In general it is best to trade stocks that are trending on an intra-day basis. For example, if you had executed a short trade in PM at FTP S2 and covered at or near FTP S3 on Wednesday, you would of experienced a much more predictable and favorable outcome.
Question 2: Should I just sell it now or wait till Monday? Will there be a potential intra-week volatility that would be better simply avoided?
Since you know what is happening with the market and your stock today and cannot predict what will happen tomorrow, you are advised to close all trades by the end of each trading day. There are ample opportunities everyday to earn money on an intra-day basis. Holding positions overnight exposes you to substantial and unnecessary risk.
Hope this helped.