Currently, it connects to bootstrap nodes and tries to discover peers asynchronously. Obviously, it doesn't handshake with the bootstrap nodes in time for it to start discovering peers so it waits another 1-5 minutes depending on the setting to try discovering again.
Startup usually takes a few minutes due to this trivial problem and an issue has been open for it since May: https://github.com/ipfs/go-ipfs/issues/5953