Im not sure you can use a timeline directly, but what i do, its to make sure my actions are done on the ReceiveUpdate event.
You use the ReceiveExecute as your “start” order, where you “reset” your parameters. After ir, the ReceiveUpdate its like Tick, you use it to smoothly interpolate yourself, one the interpolation is done, you use the Finish Execute function to end the behavior tree.
If your behavior tree needs stuff done “over time” you need to use that receive update, the receiveexecute its used at start, so if your action is instant, you can go by doing everything on that receive execute.
My attack tasks for the Deathwave game are done like that. I use Receive Execute to start shooting and setting the “target” and set the “time executing” to zero. Then, on the receive update, i count the time to run it for some time, and make sure the pawn turns to aim at the target.