SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '640357927d5f22b8bc0fbdfd9a46cfe985d3601bc91955d7532a17b4d73fe509' 
  AND token = 'C2cKtMehQUIqMxVWlN5kxDhPVIO+kN/mJGZ7aRYwAaA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}