An update.
I tested this last night to implant an xG3 (thanks @amal!) in my left wrist. I also tested the cream for one hour on my left hand knife-edge. This wasn’t sufficient. I followed Amal’s advice and re-tested with “gauze” (paper towel 
- didn’t have actual gauze and it didn’t really need to be sterile) and cling wrap. Photo below.
Leaving this for three hours produced sufficient numbness for me to perform my own insertion (this is something I’ve not been able to do in past due to self-preservation instinct I guess). It was just as numb three hours after removal as well - this is something I believe to be significantly better than the typical numbing creams used (I’m told these last about half an hour after removal?). Not sure if it’s the tetracaine or the higher dosage causing better saturation - but it works great.