Encontrei este post que funcionou para mim. Diz:
at first you must set value of "Attributes" = dword: 00000002 in [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Power\PowerSettings16b95f-f776-4464-8c53-06167f40cc99EC4B3A5-6868-48c2-BE75-4F3044BE88A7] , and then in "Power Options" - "Advanced Power Settings" in the "Display" item appears "Console lock display off timeout" in which we set the necessary time.
Espero que ajude.