If we assume the starting time is midnight one day, and they have to set off at midnight the next day, how many bacteria will we have at 00:30? How many at 02:00? How many at 23:30?
Since there is a half-life of 10 minutes (which means that every 10 minutes half of the molecules of $X$ disappear), you can probably ignore most of the $X$ produced until near the end of the 24 hours.
You will need an estimate for the volume of Rudolph's nose. You might like to model it as a sphere. You might find this webpage helpful.