SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b51f8bad63947d60beb1bf1c64ff160478ff8042bcd47ee3d44c5f213647d058' 
  AND token = 'BsLlaRKrYLp4xdkllc37OFRm9RfUrdHl8g7QJg4U/20=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00036

JSON explain

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