Usually about half an hour - what i do is look at many different images of the one ship and (depending upon its location).
I try to be as accuarate as I can.
For example, The Empress of Britain was docked in Southampton when Olympic was laid up and Majestic was berthed infron of Windsor Castle in 1936.
Glad you like them - theres plenty more coming!
Gimme some suggestions within my powers lol