Modern music notation software is extensive and so can be a comparative analysis. Since they employ a lot of different interactions to write scores, due to the mass of different symbols and their combinations, we developed a method to estimate the time spent by the user in interacting with the software interface in order to perform fundamental operations. For this we applied and extended the Keystroke-Level Model by analyzing interaction percentages in MusicXML files. Our findings contribute to modeling interaction and usability/ user experience research about interaction in music notation editors. These findings can be then transferred to analyze other editors and we expect to use the method in formative analyses to reduce user studies and thus development time in the long run.