SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '76ff20ef687d0caf44162b825aef26cf441ecc255592d5c80af010863fb0b876' 
  AND token = 'B97dJLPnRDwsz7IVPzAI30wt+X3ShJ5lxKtbHYdHjEU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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