The time it takes for HCG levels to increase can vary from person to person. Generally, in early pregnancy, HCG levels double every 48-72 hours. So, if your initial level was low, it may take longer for the levels to reach the threshold where a dark pink line appears on a pregnancy test. It's important to note that the darkness of the line is not necessarily an indicator of the health or progress of your pregnancy. Some women may have lighter lines even with higher HCG levels. If you're concerned about your HCG levels or have any other questions, it's best to consult with your healthcare provider who can provide personalized guidance based on your specific situation.