I'm planning to buy nikon D3100, can i do a night photography using time in program mode?

I'm planning to buy nikon D3100, can i do a night photography using time in program mode?

I wouldn't use program at night. If you're aiming for long exposures with little noise use a tripod and manual or aperture priority mode and a low ISO dialed in. If you're planning to do shots hand-held at night without flash, also use aperture priority mode with a fast lens such as 50mm f1.4G, and an ISO somewhere between 400 and 1600 dialed in.

Depends upon what you mean by "night photography"… If you mean taking photos of well'lit buildings at night-time, I'd recommend shooting in RAW format, as RAW will take a "normal" photo, plus 1 or 2 (depends how you set RAW mode up) under-exposures, and 1 or 2 over-exposures (what you might already recognise as "bracketing"). When you come to edit these images on your pc, your software will "sandwich" all 3 (or 5) exposures together to create a balance. Have a look at the following link, which explains it better:

http://www.pentaxuser.co.uk/article/hdr-for-nightime-street-scenes-524

If you are intending taking photos of the moon and/or stars, you would use BULB mode (get a shutter cable for this though!). You might end up with streaks instead of points of light, so with a bit of skill and patience, you can pan the subject to keep streaking to a minimum.

You do night time photography using manual mode, and a long exposure, low ISO, and as Nick has said - a tripod.

The brand/model of camera you are using is irrelevant. All DSLRs can take long exposures.

At night, I'm pretty sure P mode will automatically use the flash unless you have disabled it. If you are planning on using long shutter times (like when shooting star trails and light painting) you will need to set the shutter to Bulb or whatever long shutter speed you have in mind and you can do that with M or S modes. I prefer M so that I can control aperture size too by myself.