Can I cut my nails after the sunset? Is there any ruling for this ?
There is no rule for this.
In old times, there was no electricity. Illuminating the environment and surroundings was a problem. Without sufficient ambient light, cutting nails, cutting hair, shaving, etc would spread around more dirt. One of the primary sources of what we call "dust" and "dirt" in our homes is nothing but hairs, granulated death skin tissues. So, in order to prevent or reduce undesired dirt at home. In worst case, this dirt may may even get into food and water in dark. People would had done these kind of sensitive body care works in the daylight. This stayed as a rule and reached to today.
If your house is lightened well, there is nothing to be afraid of cutting nails at night.
There is no rule for this. People are superstitious about cutting nails at a particular time of day. There is no harm in cutting nails at any point of time. However, Prophet Mohammad (S.A.W) used to cut his nails on fridays. So a Muslim should try to cut his nails on fridays, but if he can't, then there is no harm in doing this on any other day. This is just a superstitious belief that we Muslims have gotten.