noun, adverb
A polite, somewhat formal expression referring to a specific past or future occasion previously mentioned. Often used in business or formal correspondence.
その節は大変お世話になりました。
Thank you very much for your help at that time.
またその節はよろしくお願いいたします。
I look forward to your continued support on that occasion as well.
その時 is a more general and neutral way to say 'at that time', while その節 is more polite and formal.
あの時 refers to a past time more distant from the speaker, while その節 can refer to a previously mentioned time, past or future, in a polite context.
Combination of その (that) and 節 (occasion, time). The use of 節 to mean 'time' or 'occasion' is a formal, somewhat literary extension of its basic meaning 'joint' or 'segment'.