Having 2 batteries will not lengthen the recharge time... Your using X amount of Watts/h (Volt x Amp x time), and the same number of watts/h will have to be put back in. It doesn't matter whether it's recharging into 1 or 2 batteries.
Think of a 5-gal bucket of water and you use 2 gallons per minute for 2 minutes, a total of 4 gallons. With a single bucket, you'd be down to 1 gallon, or with 2 buckets, you'd be down to 3 gallons in each (provided equal use of course). Your alternator replenishes at 1 gallon per minute. It'll take 4 minutes to replenish both buckets or the 1 bucket. (assuming simple replenishing).
I do recommend reving up the engine when doing long pulls. A hand controller throttle is a good idea.
JP