How will I know if the Ropsten Merge has hit a bug?

So, the dress rehearsal merge is in 4 days….

You can check the time till merge here : https://wenmerge.com

And here I can follow the blocks: https://beaconchain.ropsten.ethdevops.io

Sooooo if it all goes to custard will that happen straight away or hours to days later? If it’s custard how will I spot that?

It feels like a popcorn and beer event but I have zero useful knowledge….