“His [Kant’s}argument for the thesis was that if the universe did not have a beginning, there would be an infinite period of time before any event, which he considered absurd.  The argument for the antithesis was that if the universe had a beginning, there would be an infinite period of time before it, so why should the universe begin at any one particular time?  In fact, his cases for both the thesis and the antithesis are really the same argument.  They are both based on his unspoken assumption that time continues back forever, whether or not the universe had existed forever.”

Stephen Hawking-A Brief History of Time 

Actually, I thought Kant’s argument states that time is part of our sensible intuition, thus one can endlessly and dialectically argue about whether or not there is a beginning or no beginning in time, but this dialectic orignates in our own minds and is not a property of what may lie beyond our minds.

In other words, there may be a timeless (and spaceless) reality out there, but we can not know it because even knowing anything at all requires our already having time and space be a precondition of knowledge.  Such is our predicament.  Or such is our predicament according to Kant.