SELECT 
  1 
FROM 
  cscart_multi_declock_keys 
WHERE 
  key_id = '3f1aa866a98fe674e50b354d28d3072e4e0097601408936e85e99d2ad8c51b19' 
  AND token = '3Quen7vU6mC2yVskEI66GIJm1Z+tVootnmGEkrCKnr4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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