You could try S3 ListObjects operation and filter the result by LastModified metadata field. For new objects, the LastModified attribute will contain information when the file was created, but for changed files - when the last modified.
https://docs.aws.amazon.com/AWSJavaScriptSDK/latest/AWS/S3.html#listObjectsV2-property
There is a more complicated approach, using Amazon Athena with AWS Glue services, but this requires to modify your S3 Object keys to split into partitions, where partitions will be the key of date-time.
For example:
- s3://bucket/reports/date=2019-08-28/report1.json
- s3://bucket/reports/date=2019-08-28/report2.json
- s3://bucket/reports/date=2019-08-28/report3.json
- s3://bucket/reports/date=2019-08-29/report1.json
This approach can be implemented in two ways, depending on your file schema. If all your JSON files have the same format/properties/schema, then you can create a Glue Table, add the root reports path as a source for this table, add the date partition value (2019-08-28) and using Amazon Athena query data with a regular SELECT * FROM reports WHERE date='2019-08-28'. If not, then create a Glue crawler with JSON classifier, which will populate your tables, and then using the same Athena - query these data to a combined JSON file
https://docs.aws.amazon.com/glue/latest/dg/aws-glue-programming-python-samples-legislators.html