In Harper Lee's To Kill a Mockingbird, Atticus Finch is a single father. As a single father, it certainly becomes evident that Atticus is unfortunately unable to spend as much time with his kids as needed, though unlike many fathers he certainly does spend as much time with them as possible.
One point of evidence showing Atticus can't spend as much time with his kids as he might like concerns the summer months in the early chapters of the book. During the summer, it's evident that Atticus is very busy at work. He drops by the house one day while Scout, Jem, and Dill are playing out front, catching them making fun of Boo Radley. He sticks around long enough to scold them and make them promise not to play any more games making fun of either Boo Radley or anyone else in the whole town. However, what's interesting is that he only dropped by to retrieve a file he forgot when he left for work that morning and just so happened to catch the kids in the act. The fact that he drops by to get something for work and then immediately returns to work can indicate he is spending less time with his kids, as we see in the following passage:
When Atticus went inside the house to retrieve a file he had forgotten to take to work that morning, Jem realized that the he had been done in by the oldest lawyer's trick on record. (p. 50)
Other evidence that Atticus does not spend as much time with his kids as needed can be seen with respect to how neighbors and relatives complain about the children's behavior. For example, Aunt Alexandra is always complaining about Scout going around in overalls rather than wearing a dress fit for a lady. Atticus's only response, indicating how trying it is for him to be a single father, especially with respect to the amount of time he gets to spend with his kids, is, "Sister, I do the best I can with them!" (p. 83)