Lanefan
Victoria Rules
While 5e might have it that way by RAW, 5e rules are far from perfect and this is a good example.It takes less than 6 seconds. RAW says you can attempt to open a lock on your turn during combat. Success and it opens. There is no penalty, increased loudness for speed or anything else. It's a normal lockpick attempt in your 6 or less seconds. That means that outside of combat, it also takes 6 or less seconds. It can't take longer or you would incur penalties during combat for rushing the attempt.
Picking a lock really shouldn't be do-able while in initiative (i.e. combat) as it'll simply take too long given 5e's very short combat rounds. (this is one of the rare instances where 1e's one-minute rounds actually work quite well)
For the purposes of discussion I'd rather not hang my hat on a bad rule, even if it is what the book says.