Hi,
I suppose it's possible that these two triggers won't work together, but I'm curious why you have two triggers to do this. Wouldn't you be able to do that in a single Custom Time trigger? In the Day tab, select "choose days" and check off days 1 through 5; in the Hour tab, select "choose hours" and check off 12, 3, 6, and 9pm. I haven't actually tested this, but it seems to me that it would work. As for why it runs at 21:36, I don't really know - that seems like a really odd time, given the times you mention. Unless maybe you've accidentally checked off minute 36 or something.