Is your question academic or specific to your home? For general & academics, there is a good discussion in a previous question linked in the comments by Isherwood: Why is turning down the heat during day and night considered more efficient?
If you are asking specific for your home, the best way is A/B split testing (as also @FreeMan suggests).
- Over a one month heating period split the days into two groups, A and B, e.g. odd and even dates. Generally you'd want them alternating, since whether changes gradually and you have a good chance of hitting the same or similar whether with two subsequent days and thus one of each split test. This way at-home holidays or weekends can be split between the two sets.
- On "A" days run the heat 24hrs, on "B" run your scheduled heating.
- Note your daily meter reading. Measure perhaps in the afternoon so as to capture night time usage plus any offset from morning solar heating. Also note the night time low and daytime high temperature from your weather forecast (outside thermometers are tricky to place due to sun, house heat and wind).
- Chart the consumption on A days over time throughout the month, chart the consumption on B days, chart the temperatures, and visually compare. If you wish you can update your question with the charts and we'll have a chance to comment on it.
There will be some variation due to outside temperature differences between an A day and the following B day, and your meter reading will be affected by other uses in the house too. But a 30 day experiment can on aggregate provide a reliable answer.
Also translate the difference in usage to actual financial difference. For this use the energy portion of your bill, not the total bill which often includes metering charges, delivery charges, connection charges etc... which are all fixed costs.
Now you have a dollar/euro comparison between the two approaches for your specific case.
Large savings also happen when you switch to a high efficiency furnace (from 50% to 95%), when you switch to the cheapest energy source in your region (gas vs electricity), and when you apply passive heating and insulation with air exchangers, solar capture etc... Then the question becomes which of those upgrades are actually worth the cost savings, but that's for a different post.