Hit Ctrl-; to add the current date
Hit Ctrl-Shift-; to add the current time
Text is the text or the reference to a cell containing text for which you want to substitute characters.
Old_text is the text you want to replace.
New_text is the text you want to replace old_text with.
Instance_num specifies which occurrence of old_text you want to replace with new_text. If you specify instance_num, only that instance of old_text is replaced. Otherwise, every occurrence of old_text in text is changed to new_text.
ISBLANK is the null check