What is the benefit of time_bucket

[刘 嘉鹏]

Hi,all:
Question: what is the benefit of the time_bucket?
For example: the cpm day metrics contains the following time_bucket:
1. 20200531
2. 2020053102
3. 202005310101
  the time_bucket is only works on skywalking, why not replace him with the 
universal timestamp with a type?
for example :
1. 1590854400 and type 1 replace 20200531
the advantage is skywalking metrics can use other display tools to display,for 
example: kibana and grafana
Evan.Liu