The process of encoding an NFC tag takes microseconds- it's very fast.
However, encoding a sequence of tags can be more challenging as many apps delay between each encode. Additionally, most apps cannot handle sequential or unique encoding where the data on each tag is different.
For smaller quantities of tags encoding by hand with a mobile phone is easy. For larger quantities- certainly in the thousands - it is better to ask Seritag to do it for you.
Reader - 14 Jan 2023