I want to describe a software task (unit of work) that could take a long time, either because it's a lot of operations (processing time) or because it has to do communication with the network and there will be some waiting involved due to latency of the communication before the task can finish.
Without making the question too technical, let's use the analogy of a person who has to do a job that will take a long time, not necessarily because it's a lot of work, but because there are uncertainties in how long it will take to get the work done.
A lengthy task is close to what I want. However, I'm hesitant that it might convey more the "hard work" meaning (lots of work), and readers won't think of the other case (where latency is the reason it takes long). Is there a single-word adjective to capture this idea?