Previously; beforehand; for some time (indicating something was already the case). Often used in formal or written contexts.
かねてからの予定で、明日そちらに伺います。
I'll visit you tomorrow as planned beforehand.
かねてよりお世話になっております。
I have been indebted to you for some time (formal greeting).
かねて準備していた資料を提出した。
I submitted the materials I had prepared beforehand.