Do NOT use Minwax Helsman spar urethane. That's a standard finish I use on osage bows, but when I finished a bamboo backed ipe bow this winter with it, it took about 6 or 8 weeks for the first coat of finish to dry on the ipe. It took another week or two for the 2nd and 3rd coats to dry. By then, the bow was sealed and subsequent coats dried normally. No problems with it a month after completion, but it took a long time to get there!
I plan to blow the dust off my air compressor and use Thunderbird epoxy for my current ipe project.