Hi there, and welcome to the Forum.
Do you mean 45 degrees Fahrenheit? If so, that's still pretty cold I would think, and would be lower at night. It would be best to wait a week or two until they are better feathered up and more able to keep warm. Also, if you could give them an electric hen in the coop at night, and plenty of warm bedding to snuggle into of course, it would help them for the first week or so outside. It's just not worth risking them getting cold at this stage, not feeding so well because cold and huddled together, and generally getting stressed and possibly even ill.
Does your coop have a run attached? If so, they will need to be kept dry when out in the run for the first few weeks as if they are rained on they will get chilled. Maybe a sheet of clear tarpaulin or plastic fixed over the roof would do the trick. They do need top be able to get out into the light during the day, you couldn't keep them shut up in a coop, but this needs to be in a sheltered place out of the wind and weather. The actual age in weeks that you can put them out very much depends on the temperature and the weather where you live, and may vary from day to day of course - or even you might have a setback when you thought spring had come and it starts to snow again!