All the US official servers are configured to have the purge window from 6 pm until 10 pm, Pacific Time. I would suggest clanning up with someone who plays during those hours.
1500 servers are on eastern timezone it sits right In middle of pvp time on pve-C server I don’t like it sitting in middle of pvp time its recipe for gankers if you want someone to help it risk those you ask.
IT should be better to have a rotating window, eg window sequence 00-04, 04-08, 08-12, 12-16, 16-18, 18-22, 22-02, …
this make possible to be present to purge …
Otherwise , which server have purge between 12-18 GMT ?
Purges during prime time only are actually a good thing for the people who work standard working hours, hence I would disagree with your suggestion. Playing single player will allow you to customize the purge hours to your needs. Starting your own server is also an option.
EDIT: Looking at your schedule 12-18 GMT, playing on the Asian Servers might be a good option. I am not 100% sure which time zone they use but using Sing time as a reference 12-18 GMT will be 08 pm - 02 am