I use this activity as a warm-up for my Spanish II class and it can be done at any point during your class.
For the warm-up, I put two infinitives on the board and their tense. I play a song and students must correctly conjugate the verb by the end of the song. If you want to be more competitive, you can have students race to see who finishes first. Another twist would be to have conjugation stations and the group to correctly conjugate the verbs first wins.