It's not really bad. The reason for my mentioning this road before explicitly was that the other side (Multan-Sadiqabad) is newly built. So in comparison, the going side is not in a good shape. It took us around 4.5-5 hours from Sadiqabad to Multan. We were driving Santro Club 2004, so I guess your alto should do just fine.
Why would you want to take shikarpur route from sukkar? I am not sure about the road conditions there but the distance is greater as compared to n5. So I am not sure if it's wise to go there.
No worries of driving after sunset. We actually drove a significant part of Sindh at night, and there was no issue.