As you have already mentioned the Japanese loved elaborate plans and to create diversions. So from their point of view what they did no doubt seems logical while not so much to us. I'm sure part of their thinking was how to even up the odds given the strength of American forces compared to theirs.

So given that Nishimura sails from Brunei and Shima from the Ryukyus to link the Northern Force with the Southern Force. Kurita had already alerted Nishimura that his Central Force wouldn't engage till the next morning after turning back around. Shima was now 90 minutes behind Nishimura at the time. Nishimura had to decide whether to slow down and enter Surigao Strait in the morning to coincide with Kurita. He decided not to but instead make a dash through the Strait thinking that once through he could engage the Americans in a night battle on the other side. He felt that a night battle played to his strength while a daylight battle to the Americans. Of course, Nishimura had no idea their plans were now bupkis. Consequently he didn't slow down, which would allowed him to meet up with Shima, and he plowed through to his defeat.

Some blame Shima for this debacle but what about Nishimura's part in deciding to sail through the Strait at night despite Kurita's message? In the end if they had come through together, in daylight, the results would have been the same given that air power could be used along with Olendorf's ships at the same time.