SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8703ea843e99bb061e74d43958c22972778d673159962c3e587c12912b12e15c' 
  AND token = 'kQp7YYE6wk0Sh5Stie/TQUMADfZtuotNy8yksMl7MFc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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