Since time stretches out to infinity as you approach a singularity, if we assume all matter started out compressed at the Big Bang, then actually it took forever amount of time for the universe to come into existence. I’m not a physicist though so I may have gotten the relativity aspect wrong.

Assuming the start was a singularity is an interesting idea. Unlikely though. Light speed is constant in all frames of ref, even in singularities. So if a bang was accompanied with a flash then the flash must preexist at a constant speed. Which makes no sense since we are saying light came into existence along with everything else at the ‘start’. The ‘start’ must have a fundamentally different nature, where even time came into existence. You see?