Aerotech delays can be so variable (in my experience anyway) that absolute precision here isn’t really that critical. After adjusting a couple dozen RMS delays with the tool, you get a pretty good feel for how large a dimple you need to drill to get reasonably close to the result you desire and what 1/32 looks like.
Adjust conservatively (-2 seconds if you want -3 for example) then remove a ‘little more’ material carefully to adjust by single seconds.
I see the variance in delays as additional reason for having repeatable consistency and accuracy. Because the errors add up. If a delay element burned 2 seconds longer, user overestimated how much delay is needed by 2 seconds, and then drilled 2 seconds too few on top of that, the deployment will trigger full 6 seconds after apogee. If it's possible to eliminate one out three sources of error, it reduces the probability of damage to the rocket (e.g. zippering).
On a real world example, I recently had one rocket badly damaged. The delay element in an AeroTech I170 took way way longer to burn through than it should have (it's specced at 14 seconds max, it was drilled down, and I still estimated it burned for *longer* than 14 seconds), and on top of that I under-drilled about 3 seconds too few. Those 3 seconds could have made a difference how much (if any) damage was inflicted on the rocket, as the speed at deployment would have been considerably lower. Ironically, the source of that 3 seconds of user error was the delay drill tool. I used a brand new drill tool for 54mm motors, just unpacked it. I blindly assumed they come out of factory correctly calibrated (now I know they don't), because CTI tool I used in the past comes out of the factory correctly pre-calibrated (CTI tool can't even be user-calibrated, it's not an option). In my case, the tool was off by at least 3 seconds.
In retrospect, while the hole looked plausibly deep on visual inspection, it was a bit on the shallow side. It should have raised red flag and I should have stopped right there. But it was end of the long day, assembling AeroTech reload out in the field on a hot day (not my definition of fun), and it just kinda slipped. Lessons learned there. IMO, I'd be much more likely to repeat that error with "drill bit + masking tape" than with the tool. Especially now that I learned to always double check the tool is correctly calibrated before using it.