Cause it took exactly 3 days in my last transfer between my accounts.
Maybe cause request was established during Christmas events, or technical support had limited human resources. Or both.
As @Geo_Eclipse_Oksaras said usually it take longer with plexes cause service not automated and need attention of customer support to a ticket.
In similar case at this forum character transfer took 1 day as usual.
Here - WTS 83m sp - #17 by Ki11er.