#SOGL V0.12 , 35 bytes "ζ¦F‘→I ]I!}Su[I:lzm≠?■しかくFail←z=?Suκ←

Try it Here! - click run, and enter the alphabet in the input box. Note that it may be a little laggy because SOGL only pauses for input every 100 executed tokens (and SOGL is quite slow). If that bothers you, run sleepBI=true in the console.

note: don't run this in the compatibility mode - it'll just loop forever.

Explanation:

"ζ¦F‘ push "inputs.value" (yes, that is a word in SOGLs english dictionary)
 → execute as JS, pushing the inputs contents
 I named function I
] } do while POP is truthy
 I execute I
 ! negate it - check if it's empty
 Su push the current milliseconds since start
[ loop
 I execute I
 : duplicate the result
 l let its length
 zm mold the alphabet to that size
 ≠? if that isn't equal to one of the result copies
 ■しかくFail push "Fail"
 ← and exit, implicitly outputting that
 z=? if the other copy is equal to the alphabet
 Su push the milliseconds since start
 κ subtract the starting milliseconds from that
 ← and exit, implicitly outputting the result

SOGL V0.12 , 35 bytes

"ζ¦F‘→I
]I!}Su[I:lzm≠?■しかくFail←z=?Suκ←

Try it Here! - click run, and enter the alphabet in the input box. Note that it may be a little laggy because SOGL only pauses for input every 100 executed tokens (and SOGL is quite slow). If that bothers you, run sleepBI=true in the console.

note: don't run this in the compatibility mode - it'll just loop forever.

Explanation:

"ζ¦F‘ push "inputs.value" (yes, that is a word in SOGLs english dictionary)
 → execute as JS, pushing the inputs contents
 I named function I
] } do while POP is truthy
 I execute I
 ! negate it - check if it's empty
 Su push the current milliseconds since start
[ loop
 I execute I
 : duplicate the result
 l let its length
 zm mold the alphabet to that size
 ≠? if that isn't equal to one of the result copies
 ■しかくFail push "Fail"
 ← and exit, implicitly outputting that
 z=? if the other copy is equal to the alphabet
 Su push the milliseconds since start
 κ subtract the starting milliseconds from that
 ← and exit, implicitly outputting the result

#SOGL V0.12, 35 bytes "ζ¦F‘→I ]I!}Su[I:lzm≠?■しかくFail←z=?Suκ←

Try it Here! - click run, and enter the alphabet in the input box

Explanation:

"ζ¦F‘ push "inputs.value" (yes, that is a word in SOGLs english dictionary)
 → execute as JS, pushing the inputs contents
 I named function I
] } do while POP is truthy
 I execute I
 ! negate it - check if it's empty
 Su push the current milliseconds since start
[ loop
 I execute I
 : duplicate the result
 l let its length
 zm mold the alphabet to that size
 ≠? if that isn't equal to one of the result copies
 ■しかくFail push "Fail"
 ← and exit, implicitly outputting that
 z=? if the other copy is equal to the alphabet
 Su push the milliseconds since start
 κ subtract the starting milliseconds from that
 ← and exit, implicitly outputting the result

#SOGL V0.12, 35 bytes "ζ¦F‘→I ]I!}Su[I:lzm≠?■しかくFail←z=?Suκ←

Try it Here! - click run, and enter the alphabet in the input box. Note that it may be a little laggy because SOGL only pauses for input every 100 executed tokens (and SOGL is quite slow). If that bothers you, run sleepBI=true in the console.

note: don't run this in the compatibility mode - it'll just loop forever.

Explanation:

"ζ¦F‘ push "inputs.value" (yes, that is a word in SOGLs english dictionary)
 → execute as JS, pushing the inputs contents
 I named function I
] } do while POP is truthy
 I execute I
 ! negate it - check if it's empty
 Su push the current milliseconds since start
[ loop
 I execute I
 : duplicate the result
 l let its length
 zm mold the alphabet to that size
 ≠? if that isn't equal to one of the result copies
 ■しかくFail push "Fail"
 ← and exit, implicitly outputting that
 z=? if the other copy is equal to the alphabet
 Su push the milliseconds since start
 κ subtract the starting milliseconds from that
 ← and exit, implicitly outputting the result