Often, when this happens I would guess-timate the remaining time and issue a 'sleep' followed by the subsequent command. Trouble is, what if I over-guessed? Wasting valuable execution time. Worst, what if I under-guessed? A kicked off subsequent command could likely fail and the overnight opportunity would be wasted. Had I anticipated this situation, I'd simply have created a script with each step and the timing would work itself out. Unfortunately, I hadn't done so and stopping and restarting the command sequence seemed undesirable.
The 'kill' command seems to be the answer.
The steps include:
1) issuing the 'ps -aef' command to identify the process id of the command you wish to wait for
2) write an interactive script, or script file if you wish, that loops waiting for that process to complete
3) run the subsequent commands
Start by running some long command;
Open an independent terminal and identify the process id of the 'long command';
$ ps -aef | grep longCommand
user 8186 7903 0 21:34 pts/2 00:00:00 /bin/bash ./longCommand
user 8207 8195 0 21:35 pts/17 00:00:00 grep --color=auto longCommand$
Then, wait for this process to complete;
$ while kill -0 8186; do sleep 5; done; echo "done"
Followed by running whatever subsequent command(s) you wish.
The following video demonstrates this for your amusement.
Hope this helps.