SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8e7cabb4d5b0ba7865e9731d8726411b55cd761c8e05aab66d90ddc6ba9c16c4' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00031

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}