SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c21f232d4951192bb71f573f47e9951721f9ad6a1e6f6c87683e3d3ccd909304' 
  AND token = 'NZ1QPpfTfj8O3vph+ICF552yWbyly+SBlSzxKZUqDnk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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