たいてい means usually

You can use it to talk about your habit. For example:

わたしはたいてい朝早く起きます。

I usually wake up early in the morning.

日曜日はたいていゴルフをします。

I usually play golf on Sunday.

だいたい means approximately; mostly

For example:

だいたい５分で着きます。

I will arrive approximately in 5 minutes.

だいたいわかりました。

I understood mostly.

It will be mostly sunny tomorrow.

As you can see, they can possibly be used interchangeably when you mean 'mostly' or 'usually'.

日曜日はたいていゴルフをします。(I usually play golf on Sunday)

日曜日はだいたいゴルフをします。(I mostly play golf on Sunday)

They basically mean the same thing, right?

But だいたい has wider meanings, which can't necessarily be replaced by たいてい.

For the above example,

だいたい５分でつきます。(I will arrive approximately in 5 minutes.)

If you say たいてい５分でつきます。(I usually arrive in 5 minutes), it changes the meaning completely.

Hope it helps!