I've done several 24 hour tests, and typically void over 6000ml. Your sample should be stored in the fridge. I realize you are not in the USA, but they still should have given you containers, as the containers are brown to prevent chemical changes due to light. (Like green bottles are used to prevent degradation of red wine and olive oil.)
The test is done primarily to assess kidney damage.
From John Hopkins https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/24hour-urine-collection
A 24-hour urine collection helps diagnose kidney problems. It is often done to see how much creatinine clears through the kidneys. It’s also done to measure protein, hormones, minerals, and other chemical compounds.
Conditions that can cause kidney disease include:
- Diabetic nephropathy. This happens when someone has uncontrolled diabetes. It causes high levels of protein (albumin) in the urine and can lead to kidney damage.
- High blood pressure. Abnormally high blood pressure can lead to lasting (permanent) kidney damage.
- Lupus nephritis. Lupus is an autoimmune disease where the immune system attacks the kidneys and damages them.
- Frequent urinary tract infections.
- Prolonged urinary tract blockage.
- Alport syndrome. This health problem causes vision and hearing problems, as well as progressive scarring of the kidneys. The syndrome is passed down through families.
- Nephrotic syndrome. This health problem has several different causes. Symptoms include protein in the urine, low protein in the blood, high cholesterol levels, and tissue swelling.
- Polycystic kidney disease. This health problem causes the growth of many fluid-filled cysts in the kidneys. This makes the kidneys larger. Over time, it takes over and destroys working kidney tissue.
- Interstitial nephritis or pyelonephritis. This is an inflammation in the small structures in the kidney. It’s often caused by infection.
- Screening for preeclampsia in pregnancy. Preeclampsia is a dangerous health problem that sometimes occurs in pregnancy. It causes high blood pressure and can lead to organ failure.
- Kidney stones (nephrolithiasis). Kidney stones form because of an imbalance of minerals, salts and water in the urine.
There may be other reasons for your healthcare provider to recommend 24-hour urine collection.
From Mount Sinai Hospital https://www.mountsinai.org/health-library/tests/urine-24-hour-volume
You may have this test if there are signs of damage to your kidney function on blood, urine, or imaging tests.
Urine volume is normally measured as part of a test that measures the amount of a substances passed in your urine in a day, such as:
This test may also be done if you have polyuria (abnormally large volumes of urine), such as is seen in people with diabetes insipidus