I've noticed when heating up the hotend to maximum operating temperature to tighten the nozzle against the heat break, after putting a wrench on the heater block, the temperature of the heater block drops by as much as 60 °C. Do you ignore this or have a procedure to correct?
Mitigating "heat loss"
Technically, we don't lose heat, we have a drain of thermal energy out of the parts, but let's stay simple.
To combat the loss into the holding/steadying wrench, I use a vise: it might lessen the heating curve by the added thermal mass if used bare, but by adding two pieces of wood on either side of the heater block, I can insulate the block against the thermal drop from the steadying vise and atop that prevent scratches.
If you use an adjustable wrench for the heater block, one can add wooden "soft jaws" with a little cyanoacrylate glue, otherwise, some painter's tape or Kapton might aid.
It might help that my small wrenches have a super sturdy surface coating making them rather comfortable to use when left out in the cold and prevents rust. This layer also seems to prevent the flow of thermal energy into the wrench. Note that they are not chrome-plated but more like an enamel-look, a glassy powder-coat or actually lacquered.
When I need to mount something installed on the printer, I do the tightening as quickly as possible - the temperature of the measurement point and the temperature of the nozzle getting pressed into the heartbreak do not drop in the same instance, the nozzle will still be at the aimed for temperature when the thermosensor already has dropped.