After eBay fees, PayPal fees and shipping, you'll be out approximately $100 from the sale price. The further we get from 4/10, the less interest there will be from eBay buyers (trust me, I've been down this path dozens of times). You're already only getting $150-200 more for the watch, so you're looking at a maximum potential profit of $50-100, and possibly less.
Seeing as moral and immoral are RELATIVE (they mean different things to different people), I'm going to add that buying two watches with the intention of keeping one and selling the other is wrong. You're not giving up anything for the money you get, you're just taking advantage of th fact that you were already ordering one watch and you had a favorable position in line. That's wrong to me, but you do what you want. I'm getting mine 4/24 and I'm really excited. I considered selling my position and waiting a few months, but I decided $100 is not worth my waiting time.