SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a2d503dee05858e8b84d6f741fa0ab7f03864f11f777c19b2474478f043317be' 
  AND token = 'MSmHGeoBuEFbbpMYHYlFAgVsajgGbQNsbKurWtA2MxA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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