Hmmm ok, meaning i can manually clear it or i have to complete the NDL
timing? Before i could surface?
ehh.. no bro..
NDL stands for "No Decompression Limit" (remember your dive table? Your dive is limited by depth and time).
If you dive beyond the "No Decompression Limit", your dive becomes a "Decompression Dive" (deco). Once your dive becomes a deco dive, you will need to perform "Decompression Stops" on top of your regular safety stop. Depending on several factors, your dive comp will calculate the required decompression stop time... The stop can range from a few mins for most rec dives to a few hrs for some technical dives.
Clearing your deco obligations means you physically staying at the required depth, completing the decompression time as per calculated by your dive comp. You cannot press button on dive comp to "clear".
If you fail to complete the required decompression stops (ignorant to it or not enuf air/gas), you risk getting "decompression sickness" (DCS). In such case, the dive comp will lock out (refuse to work) thus preventing you from diving for the next 24hrs (assuming you did not actually end up in a decompression chamber).