[Task]: Seconds per milestone should be conditional on the network

### Task description

Currently we have a constant for the seconds per milestone that is used in certain calculations. However, this is different on each network and can change. Therefor we should expand this constant, or make it configurable from outside the wallet.

### Requirements

- Refactor seconds per milestone constant

### Creation checklist

- [ ] I have assigned this task to the correct people
- [X] I have added the most appropriate labels
- [X] I have linked the correct milestone and/or project