How long it would normally take me from landing to get out to landside, including immigration/customs/baggage?
Arrival is Lufthansa on Monday around 5.00 pm

Immigration: My experience here is as a US citizen who's always sitting in the front of the plane. Typically it takes less than five minutes; if multiple planes land at once, maybe 10-15 minutes tops. There's about a five-minute walk from the gate to the immigration hall, depending on which gate you arrive at. YMMV if you are not a US citizen/permanent resident or if you are sitting far back in the aircraft.

Baggage: I rarely check bags at all, but when I have done so, it can take a fair amount of time (up to 30 minutes waiting around in the most annoying cases). PHL--my home airport--is fairly notorious in this regard. This is one key reason that I don't check bags.

Customs: no time at all unless you have duty to pay. You just hand your form to the official on your way out of the baggage hall.

Yes, as Travelmad478 said, it all depends on:
Are you a US Citizen?
Will you sitting close to the front of the plane?
Was there more international arrivals at the time when your flight landed?

It can all take just 15 minutes or so if you are lucky........
i have been there almost a hour and a half before getting out with bags.

I'm not US citizen, travelling on visa waiver.
Sitting in the front. Will have a couple of checked-in bags - priority baggage, but I'm not sure if it makes any difference in PHL.

I would budget at least one hour to complete immigration, customs and baggage collection. (in case you have plans for the evening).

Thanks!

I agree with snod08. About an hour sounds right.