Tuning Cartographer to identify free space at earliest?

[elanchezhiyan-official]

Issue:
so when i run cartographer slam, I get a slam map, which has its map.data filled with [-1, 75,etc ] representing obstacles and unknown space, but after a timeline of about 5 minutes, it detects the free spaces that is "0" value is observed in map.data.

Map.data at time of 5 seconds after launching cartographer,

Same map after 5 minutes,

As we could see, after 5 minutes, we can observe free spaces in map.

Solution For:
Is there any technical way i could reduce this time period that is required to identify the free spaces and reflect them as "0" in map.data,

I know that this might come at a cost of someother inefficiency, if you could help me about it,Please detail,
Thank you.