A Little While Ago, Earlier In The Day, A Short Time Ago
noun
The previous extent of time was a little while ago. Just think to a previous extent of time that was indeed a little while ago. Now, associate! 先程 is limited to a relatively brief time frame within the same day. So it can be used for something mentioned earlier in a speech or at an event from earlier in the day, but not for something from a few days ago. 先程 is also polite and formal, so it's generally used in professional or respectful settings.
さきほど
The reading is the words 先 and 程, put together.
あれ、先程コンビニもでお会いしましたよね？
Oh, we met earlier at the convenience store too, didn't we?
先程からあそこに座っているご老人はだれですか。
Who is the old man sitting over there from a little while ago?
先程も申しましたように、お客様の予約はキャンセルされました。
As I told you earlier, your reservation was cancelled.
先程あなたからの手紙を読ませて頂きました。
I read the letter from you earlier today.