My answer is "it depends". Are you wanting to continue to improve the number of pushups that you can do? If so, then keep increasing the number per day. If you want variety, change the type of pushup each set. If you are pursuing strength, switch to harder variations.
I would also consider doing a pull to balance out all of the pushing. Especially if you plan to continue this challenge for a number of days/ weeks.
I hope this made sense and was helpful!