Commented by: @cincuranet

There's redesigned transaction options param. Now it holds transaction behavior (=old options) and new property for timeout (and it's open for future improvements). So now you will start transaction i.e.
conn.BeginTransaction(new FbTransactionOptions() { TransactionBehavior = FbTransactionBehavior.Wait, WaitTimeout = 3 })
.
The rest is same.

When you wanna to use timeout, simply set it (must be >=1). If empty (null), it's not used (important for FB1.5).