SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '3f6d38ee11091c377eb7c1abd3a0d710f003985e00f612d7152af37139144d5f' 
  AND token = 'Kgu07XZuW8HziDDSHY+uE17YdJzUdCs9aWSApVmtDmE=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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