Two cleared jobs at once

Is there any downside to accepting two cleared jobs at once , stalling on starting one and ultimately starting the other one? It would be in order to make sure that the ultimate job worked at is a good fit. What happens when two employers both try to have the clearance transferred?

From my understanding, only one investigation can go on at a time.

I thinks its highest takes precedence (t5>t3) and oldest open date takes precedence after that.

No I meant already having the clearance, getting more then one cleared job offer, and accepting more then one before deciding on one job.

Or having a day cleared job and a second part time or weekend cleared job. I that allowed?

What does t3, t5 mean?