SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '5a21720275c45d0007b891524b2d528f9002db63311af22bda4a6c70c68b0833' 
  AND token = 'xYabFYKvLqAKGzXzyeOTMkY2cIsoreRcbxdz3AnV/cI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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