Get Grafana metric data via API

Hi Team,
I am using this API to get metric data
http://ip-address/api/datasources/proxy/1/api/v1/query_range?query=node_filefd_allocated{instance%3D"ip-adress%3A9200"}&start=1619700030&end=1619703630&step=15
but in this query we have limited timestamp because we have specified start and end time but we need to get real time data. I have also tried using now function but it is not working.
Also not able to get cloudwatch metrics from grafana
Could anyone help me on this?