Install "at" on Ubuntu

sudo apt-get install at

Commands in a file - relative time

Save your commands in a file. e.g. run.sh will look like this:

date > a.txt
whoami >> a.txt

Then schedule it to be execute a minute later:

at now + 1 minute < run.sh

Run without file - relative time

echo "date > b.txt" | at now + 1 minute

A minute later you can check your file system. You'll see a new file called "b.txt" with the date in it.

Run without file - absolute time

echo "date > c.txt" | at 04:58

At 04:58 the file c.txt will be created with the timestamp in it.