The slack import tool currently imports all message data. However, for large datasets that span years, this can take a while to import all the data. Additionally, it's likely this won't fit within a free tier DB if they've been running for years.

For both of these, we want to add a --since flag that can be used for this. It should accept both date strings (YYYY-MM-DD) as well as relative times (7d which would mean 7 days ago) to allow flexibility in usage, where tiger-eon might do --since 1m to import the last month of data.