So, if I get you correctly, you are suggesting that if there are multiple self-existing things, and if they don't interact, time wouldn't exist. I agree, if ALL of them are causing nothing.
{Yet even then, they are all under one umbrella principle —the existence of all of them. Which, at least to first cause, is then impossible, for their existence is existence apart from the causation of first cause, which is impossible, because there is no principle external to first cause by which first cause must be affected —in this case, the existence of external existences, when he is the first cause of the principle of existence itself.
So, if there is first cause, (and we should agree there is, or we would not exist), there cannot be multiple self-existences.
I had at one point thought that
@Ken-1122 was claiming there could be multiple self-existent things that did not have any effects, but I found out he was saying there could be multiple self-existent things that do have interactions with each other and effects. Thus, if there are effects, there is cause, and first cause (to me logically) is necessarily implied.}
But in writing this, I'm beginning to see what you are getting at, which applies to
@Moral Orel 's claim that multiple self-existences had no beginning (which he defines as past tense only), and to this you are saying his definition is meaningless, unless at least one of them causes time. Nice.