Not sure if you can use this but if you simply want to convert that to a readable date, you can use:
date -d @1440604784 +'%d.%m.%Y'
The output would be:
26.08.2015
Thank you. I used another approach, but your idea helped me to find the right solution for my issue.
e.g. (output truncated):
bitcoin-cli listtransactions | jq '.[].time |=(. | strftime("%Y-%m-%d"))'
Result:
{
"txid": "5756ff16e2b9f881cd15b8a7e478b4899965f87f553b6210d0f8e5bf5be7df1d",
"blockhash": "0000000000000000027d0985fef71cbc05a5ee5cdbdc4c6baf2307e6c5db8591",
"blockheight": 371622,
"confirmations": 160829,
"time": "2015-08-26",
"blocktime": 1440604784,
"isCoinBase": true,
"valueOut": 25.37726812,
"size": 185
}