When a file is downloaded, the application only downloads the minimum number of shards required to reconstitute a file. If your node is offline when a download is attempted, the network will route around your node, and download shards from other nodes. If your node fails to respond to a valid download request, you will not earn STORJ for the egress bandwidth and your node reputation will be impacted.
To be considered a reliable farmer, you should keep your uptime above 99.3% which translates to a maximum of about 5 hours 6 minutes and 48.2 seconds of downtime a month.
Please, read more in the blog Early feedback from V3 storage node operators: You’ve got questions, we’ve got answers!