There are many, many different versions of sepia toning. For example, two different versions can be seen in this old thread:
https://www.photoshopgurus.com/forum/photoshop-newbies/56172-how-do-make-picture.html
Specifically, one can:
a) Leave some fraction of the original color in the image, but add a sepia wash over everything;
b) One could convert the original to B&W (ie, so that there is none of the original color left) and then add a sepia wash over it.
These are the two techniques that Sam and I described in the old thread cited above. Other possibilities include:
c) one could add sepia only to the midtones, leaving very dark and very light tones with no color (...this approach was popular a few years back);
d) for a more subtle effect, just add color to the blacks and darkest tones; or,
e) a technique popular with wedding and engagement photographers stuck shooting on an overcast day with a white sky is to just warm up the lightest tones (ie, especially, the sky), etc. etc.
One typically uses different Photoshop tools to get these different effects. These include:
the photo filter (with "preserve luminosity turned either on or off - you'll get different effects);
putting a solid sepia color layer at the top of your layer stack and set its blend mode to multiply, color burn, or something similar;
using the curves tool, or less flexibly, the levels tool;
using the hue / saturation tool in "colorize mode";
using the BlendIF sliders on any of the above;
making a duotone or tritone version of the image;
etc.
I realize that you said you didn't have time to experiment, but, to be honest, if you want to be happy with the result, you will probably need to do so. The reason is that often it's difficult to a priori visualize what some people would consider subtle differences between the above versions of sepia toning, so the only way to choose is to experiment with each of them. Once you are familiar with them, the differences will be obvious and you can use that skill you just learned and the associated eye training for many other photoshop tasks.
HTH,
Tom M
PS - After seeing Chris's very nice example, one further thought: I have found that you'll often get a much nicer sepia toned result if you adjust the contrast or the image's black and white points. Without doing that sometimes using the above techniques can result in murky images. Also, depending on the starting image, sometimes it's better to convert it to B&W by using all the adjustments that a B&W adjustment layer gives you, not just desaturating the original.
