Notify that function Now() returns time AND date (help says "Now returns the current date and time, corresponding to Date + Time"), so if you try to convert it to HH:MMS value, convert error comes up. Result is clear - value which is rendered on screen is still same (beacause of date included in outcome Double value). To avoid that, use only Time() function to get current time, or Date() to get current date, or Now() to get time and date together.
I hope that I explained it cleary. If I didn't, I'm sorry