ideally you should pick a time period, say from lunch to dinner, don't have any lunch and of course, no novorapid insulin...........test your BG, try not to correct unless your dangerously high, record.
you can test as many times as you want between lunch and dinner but on Lantus you would be fine with just a test at lunch and one before dinner.........this tells you if your Lantus dose has held you steady, ie between 1-2mmol. If so your dose it good between lunch and dinner. if its not, you will need to consider testing the rest of the day , overnight, dinner till bed etc, as your on a single dose, changing the dose for just 5 hours of 24 may have effects on the rest of the day.....
this is the basics and the start..........I would prefer to start basal testing overnight, your dose may be out by then though......