Just started fermenting a Patersbier last night. Currently have a bubbler airlock in the lid. I want to replace this with a blow-off airlock. Is it ok to replace this just 24 hours after fermentation has begun?
yes, you'll be fine. Sanitize it well, and make sure your hands are sanitized. There will already be a layer of co2 that will prevent o2 from reaching your nectar.
CO2 is heavier than O2, and there should be thick layer of CO2 on your beer by now. You will be fine as long as you are gentle to your bucket and everything has been sanitized properly.