Currently, it takes around 10 seconds to right-click your crew member in the garage, click on the "Reset" button, then select the free retraining, since the current default is to use up one of your retraining orders. If you need to switch tanks, that might be another 10-20 seconds, so let's be generous and say we can reset three crew members a minute, 180 an hour. If you have 1000 crew members then you'll spend around 5½ hours total doing mindless clicking, with a high risk you accidentally use up one of your retraining orders.
Choosing the additional skills for all those crew members will take more time obviously, but at least the reset portion is done before the 30-days are up.
For a better experience, we request that you give us the option to reset all our crew skills in one go. This gives us more time to play the game and experiment without the stress of a ticking clock. To avoid issues previously encountered during Crew 2.0, we would like this button to be present in the current Common Test to ensure that it doesn't negatively affect zero-skill crews, for example.
Source: https://www.reddit.com/r/WorldofTanks/comments/127uqqb/request_please_give_us_a_button_to_reset_all/