I really am having to struggle to get my surveys looking professional and not spreading out over huge pages and many pages.

One issue is when I ask for time, as far as I can tell, I need to enter Hours and Minutes in separate text responses.  These appear to have to be on separate rows (and with the default huge padding--an issue covered in another post).  (Likewise, I don't want the unnecessary and garish green instructions.  I've posted a separate question about that.)

Is there any way to get them on the same row?  See attached. 

I think you need to consider mobile devices - single columns are better on those devices.

The way LimeSurvey works is that multiple columns are automatically shifted to single column on any device with a narrow screen. Thus I do not need to design with mobile devices in mind nor to I have to create surveys for use on desktops and laptops that only look good on cell phones.

As this is a question of type "multiple short text" this is the desired behaviour.
If you search the forum you will find a solution to merge two questions.
As far as I remember this solution is for drop-downs, but can be easily changed to text input.

By the way, you mentioned that people are used to enter time as HH:MM.
So why don't you let them enter the time this way? 
One "short text" question.
As you have to validate the input anyway, you can this do here as well, with a regular expression and/or mask input.

 

That sounds great! Since your suggestion is not one of the standard options in LimeSurvey, could you give me a hint at how to create a mask? All I want is a text field with a ":" in the middle that only accepts numbers (2 digits on either side of the ":"). And which field in the question "characteristics" (I forget what that column of menu items on the right is called.) I would enter the mask into.

Maybe related, is there a way to enter a default into a text field? I could enter a default of "00:00" and let the respondent change the numerals.