If your custies have your mobile no' then i would leave a message on your voicemail, i.e running late due to holiday.
I wouldn't worry, i use to, but most custies, don't even know if your early or late.
You get the odd one "i thought you'd given up!" after about 5 years they stop saying this.
I've stopped appoligizing for being late; as you get some "oh that's alright i'd rather have it done less often"
Only explain if askes