Hi @shankar ,
I faced the same issue a couple of days ago. Unfortunately, it is not possible to filter by lastModifiedTime. However, it is possible to filter by Modified 😀
https://graph.microsoft.com/v1.0/sites/example.sharepoint.com:/sites/development:/lists/5e6d49c5-b4a2-4fe0-9e08-15b6da8a929d/items?$filter=fields/Modified eq '2020-07-08T08:23:03Z'
Can you give it a try and let me know if it works?
Regards
Jarbas Horst