You’ll need to bear arms to eat at a Denny’s in an urban environment after midnight.
In Houston the local Denny's and House of Pies (local chain) have the Blue-and-White Seal of Approval, with plenty of two-tone city cars parked on the lot Code 7 after about 3 a.m.
Very bad idea to stick either of these places up in the wee hours. Also, Andy's in the Heights, favorite Tex-Mex greasy spoon and favorite source of early-morning indigestion.