SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '4b0236b84aa28670aa9c2c55da95fa52995d056b3c21cb0abea5e778d749a467' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00017

JSON explain

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