Bitcoin has no hardware requirements on its own, its the miners competing with each other that causes difficulty to grow.
The minimum difficulty is 1 and even at that level (without it going up) you can't mine blocks on 10 minutes average (or close to it) on a very old computer with a weak CPU.
The first block took 5~6 days to mine,
That is a very special case which you can not use to determine Satoshi's hashrate. He basically created that block hardcoded it in the software then released the software 6 days later when block #1 was mined.
You are also ignoring the fact that time between blocks 1+ isn't that long.
For example:
Height: Time
1 2009-01-09 02:54:25
2 2009-01-09 02:55:44
3 2009-01-09 03:02:53
4 2009-01-09 03:16:28
5 2009-01-09 03:23:48
6 2009-01-09 03:29:49
7 2009-01-09 03:39:29
8 2009-01-09 03:45:43
9 2009-01-09 03:54:39
10 2009-01-09 04:05:52
11 2009-01-09 04:12:40
12 2009-01-09 04:21:28
13 2009-01-09 04:23:40
14 2009-01-09 04:33:09
15 2009-01-10 04:45:46
16 2009-01-10 04:45:58
17 2009-01-10 05:03:11
18 2009-01-10 05:12:14
19 2009-01-10 05:22:54