If I understand your question correctly, you are trying to export a single value to an excel spreadsheet. The function you are using to write to the spreadsheet takes in a "1d" which means that it expects an array input, not a single value. If you really just want to write one value to a spreadsheet, you can insert a "build array" function and turn your single value into an array which only has one element and it will work.
However, this is typically not how you use a the spreadsheet function. The spreadsheet function is meant to store a lot of data in an array to a spreadsheet to be read by excel. If you really just want to write a single value to a file, you only need to write to a .txt file. If you want to create a long list of values of the time durations between the pulses, build an array of values using a shift register and when you are finished, write the values to the spreadsheet file ONCE at the end. If you don't find the time delay associated with writing to the file on each cycle, you can also write the same array to the spreadsheet file each time you aquire a new value.
