search for: start_of_experi

Greetings, My data set has dates and times that I am working with. Some of the times in Time_of_end are blank. This is supposed to dictate that the particular experiment lasted 48 hours. I would like to add 48 hours to the start Start_of_Experiment for another column as End_of_Experiment including both the ones with 48 added and those with early times. I was thinking something with a conditional statement but I can't seem to figure out what code to use. Any insight would be appreciated. Let me know if there is anything else you nee...