Work 5 hours or work for 5 hours

[NAL123]

Consider these sentences of mine, please:

1) Yesterday, I worked for five hours.
2) Yesterday, I worked five hours.
Also
3) I've been working here for twenty years.
4) I've been working twenty years here.

Can I omit 'for' in each case without changing the meaning?

 

[emsr2d2]

1) Yesterday, I worked for five hours.
2) Yesterday, I worked five hours.

In BrE, you can't omit "for" in that context.

3) I've been working here for twenty years.
4) I've been working twenty years here.

4 would be OK if you moved "here" to after "working".

 

[Skrej]

#1, 2 and 3 are fine in AmE.
#4 would work with the position change suggested in post #2.

 

[5jj]

In BrE, you can't omit "for" in that context.

I find I worked five hours yesterday natural enough.

 

[emsr2d2]

I find I worked five hours yesterday natural enough.

Interestingly, so do I. However, that's not the word order in post #1. For some reason I can't put my finger on, it feels off with "Yesterday" at the beginning.