SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c51715f0d8fe834a9653f822471b0a8d6ec5a09739134d045cd58eece0fbc51f' 
  AND token = 'AndZyRMUFgrMzjDuvQ+wTypCCn/shhNXqj4MATouPlM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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