I haven't bumped into the issue yet, but I know it does happen from time to time. Some have said the format of the video you upload can have an impact on the processing time.
my last 1080p video (29 minutes, 2.13gb) 60fps, 10,000 bitrate, took about 70ish minutes to upload via my mobile (my upload speed on my regular modum is 1mbps... ouch)
the processing was super quick. generally takes less than 5-10 mins. but I upload as .mp4 so I think it's exporting at an already optomised setting.
I wouldn't trust an online provider of any kind to process files into other formats quickly, which is why I also export to youtube friendly format before uploading and it's always super quick to process. I'm sure I'll be impacted by it at some point.