SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a50688c836083620baf210db608e4d415cb2c33e318904f4edf1957db5cace32' 
  AND token = 'SKkNt9uLltg7ZRsoY55vA/Uu/xKbvHgmQjVZYHHdYoM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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