There are a few important factors that you left before answering this question:

1. What is your gardening zone?
2. Is the direct sun morning, noon or late afternoon?
3. Is the location otherwise sheltered or is it very exposed and windy?

I also planted by japonica under the shade of two deciduous trees (maples). So they will be getting a good deal of sun in winter as my house faces south/south-east.
Just moved here and brought the japonica with me--so it'll be the first year in this locale. ( I just planted it a couple of weeks ago and it's fine.) Come to think of it, I didn't even consider winter sun when planting it! But winter sun IS an important factor because broadleaved evergreens can get sunburned by winter sun. This is especially true in February or March. Why? Well, if the ground is frozen and it's really cold, the sun even at this time of the year can warm the leaf enough to burn--and the plant can't get enough water from the ground (because it may frozen). You should be able to plant the japonica in the locale you are considering though if you do the following:

1. Plant it as soon as you can (as long as it's not really hot). Look at the extended forecast--if temps are in the 80's, it'll be okay--especially if it's humid (considering it's in shade).
2. Be sure to water in well.
3. Mulch the plant.
4. In November, spray it with an antidessicant (spelling sorry). Available at any good garden center. This will reduce the amount of water the plant looses on those sunny but cold winter days. I don't think you (we) will have a problem.
5. If necessary, water the plant thoughout the autumn if the weather is dry. Water during mild periods of the winter (if the weather is dry)

I have grown A.j.'Gold Dust' under deciduous trees for 20 years and also in an open area that receives annual morning sun until noon, all are very robust and none have suffered from leaf scorch. I have had seedlings appear in areas that receive afternoon sun and apparantly suffered no ill effects, but were removed because they interfered with other plants. Most authors rate hardiness to Zone 7, but there are references that indicate Zone 6.
Once established, they are a really tough plant and withstands extreme heat and drought.(thoroughly tested here, this year!). Don't know about extremely dry cold, as I wasn't growing them in the mid 1980's when our temperatures dipped to -12°F.for a couple of nights, but have experienced no problems with temperatures at or slightly below 0°F.
Rb