Hours conversion into "day shift" & "night Shift"

I am encoutering a few issues with the following:

I would like to have a formula to tell me this is night shift or day shift.

Day shift starts at 6:59:59
Night Shift starts at - 19:00:01

So for example what formula would i use if I had <TABLE style="WIDTH: 87pt; BORDER-COLLAPSE: collapse" cellSpacing=0 cellPadding=0 width=116 border=0 x:str><COLGROUP><COL style="WIDTH: 87pt; mso-width-source: userset; mso-width-alt: 4242" width=116><TBODY><TR style="HEIGHT: 12.75pt" height=17><TD class=xl23 style="BORDER-RIGHT: #ece9d8; BORDER-TOP: #ece9d8; BORDER-LEFT: #ece9d8; WIDTH: 87pt; BORDER-BOTTOM: #ece9d8; HEIGHT: 12.75pt; BACKGROUND-COLOR: transparent" width=116 height=17 x:num="40182.990393518521">
Mon04/01/2010 23:46
</TD></TR></TBODY></TABLE>

Thanks for you help.

Shan