Since there are no clear dates so far in C&D, we'll have to use estimates of the characters ages in the flashbacks and present day (which isn't difficult based on them being in high school in present day). I'll use the child actors who played the roles in the flashbacks to gauge intended age of the characters in those flashbacks, while also accounting for the fact they filmed this stuff probably close to a year ago.
So, Maceo Smedly who plays young Tyrone was born in Feb, 2007, and the Pilot episode was filmed in Feb 2017 so the actor was ten years old, likely indicating young Tyrone is around 8-10 years old in the flashbacks (child actors often play roles a couple years younger than their actual age). The actress who plays young Tandy (Rachel Ryals) doesn't have a birth year listed on IMDB, but according to her bio she began acting at 8, and her filmography only has a few roles, the earliest releasing in 2018. Given the filming date of early 2017, I'd imagine the actress is also between 8-10 years old at the time of filming. Not exact details, but helps narrow things down at least.
As for what year the present day stuff is set, I can't say. 2016? 2017? 2018? As TalonCard pointed out its during high school basketball season, but that doesn't narrow things down much. Practice begins in early September for Louisiana high school sports, according to this link, as all other estimates are drawn from (there's no reason to think the dates have drastically changed in a few years, depending on when exactly C&D Season 1 begins).
Link
This means C&D can begin really anytime during school year before March, so September to February (even March in case of finals).
I'm watching the first episode now and at 1:05 the front end of a white Lexus can be seen. Does anyone familiar with autos recognize the model and possible year of that vehicle? that could at least provide and earliest possible placement for the flashback scenes.
The flip phone Talon mentioned that Tandy is using (at around 1:45 mark) could also help narrow down likely intended placement, least a bit. Tandy's dad also uses a Blackberry-like device shown very quickly at the 3:37 mark.
At the 7:43 mark, Tandy's father's work ID badge shows date ranges for when its issued and when it expires (presumably, its a bit out of focus). Doing my best to read it, I THINK it says ??MAR08 to ??MAR10 (I can't read the first couple of numbers that correspond to the specific day). I think it may be March 29 on second date, but can't make out the first one. Doesn't really matter anyway as it doesn't specifically denote the date of the flashbacks, but at least it narrows it down.
This indicates the flashbacks occur sometime between March 2008 and March 2010.
Given Tandy is getting into a club underage, I'm going to assume Tyrone and Tandy are in their senior year of high school.
At around the 20:30 mark, one of Tyrone's friends mentions she's throwing a party in the woods to celebrate them making state, likely placing the first episode in February (since State Championships are usually held in late February to early March, and its indicated they had just completed regular season or district playoffs). February is definitely the most reasonable spot to place the show's first episode.
As to whether thats meant to occur in 2016, 2017, or 2018, I can't say. I am however inclined to lean toward 2017 so as the show's timeline runs concurrent with the filming timeline, since thats often how the Netflix shows approach their timelines (well, sort of).
At 21:15 Tandy is walking along a road and the trees are all leafless in background, indicating winter time. Even though its set in and filmed in Louisiana, apparently it gets cold enough for leaves to fall off trees (that happens to some degree even down here in sweltering Florida, though our winters rarely dip below 40 degrees F here). This backs up the February month placement, especially as thats when that shot was most likely filmed (since first episode began filming in early Feb 2017).
At 31:13 a newspaper is shown, but the date isn't visible, or may not even be on the paper itself, another tactic I've noticed a lot of TV shows utilize is removing dates altogether in places they'd normally be, to avoid specific timeline placements for whatever reason--have a feeling thats the case here, in combination with the "Years Later" tag instead of a specific number of years.
At 31:48 a specific date is shown on a security camera feed, 2007-04-18, indicating the Roxxon oil rig disaster that gave Tyrone and Tandy their powers occurred in April 18, 2007 (which conflicts with the security badge of Tandy's father, but I'm taking the security camera date over that since its clearly visible and they had to pick a specific date for the cam feed as they always could've just used a cam shot without a date).
In episode 2, at 4:17 mark, Tyrone's father mentions "Eight years ago, fate pushed us down hard." This is obviously a reference to Tyrone's brothers death, placing the flashbacks in 2007 based on the camera date, and eight years later would place C&D sometime in 2015... we'll see.
At around 24:35 mark of episode 2, one of Tyrone's teammates mentions they're going to state finals "next week", indicating the season begins a bit after mid February, with first episode covering a few days, and episode 2 picking up following day sometime after Feb 20 or so.
At 36:20 mark of Episode 2, in a dream sequence, on a milk carton Tyrone and his brother's pictures reflect they've been missing since June 6, 2008 (6/6/08), which may be the intended date of Tyrone's brothers death and the oil rig explosion, which would put present day events either in 2016, or Feb 2017 (same as filming period), which would still be 8 years after Billy's death to tie in with Tyrone's father mentioning it was 8 years ago (or 8 years and 8 months, meaning his father wasn't rounding up to nearest year, which makes sense in that case).