Is that because of the network being fractured?
Also, is there a rough estimate of how long a transaction must be in the system to be considered more or less final?
Like in Bitcoin, there is a 3 block confirmation time and a person can be reasonably assured that transaction won't be reversed.
It's because of latency.
Confirmation time depends on TPS rate. Before TPS becomes constant we'll be using checkpoints issued every 5 minutes, so after your transaction gets more than 50% of the votes you can treat it as confirmed.