Tetsu takes about 2months for full,and after that you're in the last region (if not than you did something wrong) and in the last region it should take you about 1month to get seasinger
I've not actually done PoP yet, because I'm still getting the stats to do it all, but I've done a lot of research from my clannies, and for Tetsu you're looking around 6weeks-2months, then for seasinger it should take you another month-6weeks.
From the very beginning, it took me about three months for full Sea Singer's.
Starting from the Pincer's region, you'd be able to obtain another set quite quickly.
Well I've been doin it twice a day since it came out (at first i was litterally doing all the voyages each day) And I only have 65 plates now and I have the things built that gives more special item missions