My phone has a 4-digit pin code. While not super secure, I’m able to unlock it in anywhere from <1s to 2-3s, depending on if my fingers are cold and if I’m distracted. At worst, it might take me 7-8sec if I’m high stress (I think that’s about how long it took me to unlock my phone after I had a wreck, and that was with my arms shaking so badly from adrenaline that I couldn’t hold the phone to my ear). On a gun safe, that’d still give me a lot of time to open the door, grab my gun, load it, and find a safe place to hide.
Now, 4 digit pins aren’t super secure, especially if there’s no limit to failed inputs; a kid could probably go through all 9,999 10,000 potential combinations in an afternoon. However, if you increase that to 6 digits, you now have up to 999,999 1,000,000 combinations a child has to go through; yet the combination is still easily rememberable and the time to open the safe has probably barely increased.
Edit: forgot about 0000 and 000000 as possible combinations for 4 digit and 6 digit pins.