It is only 48 days til Christmas! And with 8 major presents to buy over the Christmas period, that only gives me 6 days to think of and buy each one. Eeek! Factor in lots of minor presents at a lower importance level, that leaves me with approximately 4.83 days per major present! Which, taking into account four days postage for internet presents being sent, and assuming that half will be bought from the internet, leaves me 2.83 days per present!!
However, given that for 5 of the 7 weeks left, I only have 2 days available to shop, that factors the time down to 1.415 days per present. Assuming the trip into town to be a round trip, my effective time is 2.415/(2*pi) which takes it to roughly 0.225 days per present, which equates to 5hrs and 24 minutes effective shopping time.
In addition, the majority of my Christmas shopping will be done accompanied by Rachel. Unfortunately, any time spent shopping with her results in a split between her buying presents and me buying presents, and (being kind to Rachel!!) I shall set that at a 1:1 ration, lowering my present time to 2hrs and 42 mins per present.
Finally the overall time T is a function of 5 variables, l, c, t, f and q which relate to the time spent reading the Christmas list, time spent consulting with other family members about who's got what, time spent thinking of ideas, time spent finding the product and time spent queuing in the shop respectively. The equation is roughly shown below.

l within our family takes a value somewhere in the region of 0.5
c is related to the number of people in the family, and is usually roughly (n-1).0.166
f can be taken as 1.
q takes either the value 0 if bought online, or the average for Harrogate shops, which is roughly 0.2. I will assume as before that half the presents will be bought online, giving an average q of 0.1
Substituting these into the equation gives an available thinking time (t) of 1hr and 25mins. I'd better get started!