SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'e7ac3c6c5d7832c54d06a460bc4d6988d2cb712b2a787de5c033d1ee5f7836be' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00031

Explain
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE Impossible WHERE noticed after reading const tables