Option to keep notes unlocked even after browser restart

Sometimes user want to use his notes without the need of entering password all the time, something like "Keep unlocked for a whole day".

The problem is that restarting browser will delete decryption keys so notes will be locked when browser starts.

Possible solutions:

1. encrypt decryption key with new random key and store the key in one of the browser storages. However this poses a security issue as the decryption key will be stored in storage, not just in the memory. So anyone with access to the files on the drive would potentially be able to decrypt everything - so malicious process or someone who found your notebook (unless your drive is encrypted). However still very unprobable.
2. create companion app that would be running in the operating system and store the encryption key in the system memory. This is how most password managers for browser works so this would be the best option. But creating a desktop app is not exactly easy - plus it would have to be written in C language to reduce memory consumption to minimum.
3. research some other options.... I think I've read about some secure storage for storing encryption keys in the browser