Insert Missing Hours

Hello,

I'm hoping my problem is easy to solve. I've got one years worth of weather data and it can be recorded at frequencies of 1 hour, 3 hours, 6 hours or more. What I need to do is fill in missing hours. So, if I have a row that has 3 AM and the next one is 6 AM, is there an easy way of inserting 4 AM and 5 AM in between? I've attached a sample file.

Also, on a similar topic, if I have times that have a period in them instead of a colon, what is the easiest way to convert them; if I do a simple replace, it changes the values because it thinks it was decimal hours; if I change the format, that doesn't work either.

Thanks for any help.