Not sure if you are asking about fetching the ad info (VAST/VMAP/SMRX) or playing the ad videos.
When playing, there are some preset limits already to make sure ad does not take longer to buffer than actual play time.
When fetching ad data, there is a timeout for each individual request, 5 seconds or so.
If there are multiple ads returned, this may still take long time. JiT fetching of ads is meant to help by deferring fetching of wrapped ads to later when content is playing.