Excellent question. i heard that the s***m need at least 48 hours to mature, so i suggest the every-other-day plan.
but do check out this excellent yahoo answer on the same topic by someone who claims she got pregnant with OLIVE OIL!!! (pre-seed didn't do the job):
"Best Answer - Chosen by Asker
It takes 70 days for s***m to be made from start to finish. We were TTC for 19 months, having sex "every other day" around my fertile time. In January we decided to have sex EVERY day around that time, and it was the month that I got pregnant. And watch what you use for lubricant, many OTC don't support the s***m well and kill them off even if it doesn't say spermicide. We used Pre-seed with no luck for 6 months. All 3 of our children were conceived using good old Olive Oil. It's very close in pH to s***m and they live better in Olive oil than in the preseed.
and here's a good article from baby hopes:
"Will abstaining from having sex help improve s***m count?
Couples who abstain from sex in the hope of saving s***m until the woman is at her most fertile have definitely been misled. A recent study provides the strongest evidence yet that not only is abstaining from sex of no benefit to couples with normal fertility, but it can also damage the chance of successful conception among couples seeking fertility treatment.
The World Health Organization guidelines state that men should abstain from sex for between two and seven days before giving a sample for fertility treatment. This however does not mean that if you are trying to conceive you might have the best sperms if you abstain from sex for a few days.
Some studies reveal that delaying ejaculation may increase the total concentration of s***m and perhaps the volume of semen. However, the percentage of normal s***m and the percentage of motile s***m decrease with infrequent ejaculation. Overall, the study concludes that ejaculation three to four times per week will ensure the optimum number of good motile s***m.
Results from a study related to abstaing from sex and the ability to conceive
A team lead by Eliahu Levitas, a fertility specialist at the IVF unit of Soroka University Medical Centre in Israel, looked at s***m samples from around 6,000 men who had abstained from sex for up to two weeks. Most of the men had normal s***m counts. Around one third of them had low s***m counts, meaning they produced less than 20m s***m per milliliter.
Researchers found that if men had low s***m counts their s***m steadily became less mobile after an average of one day's abstinence. Their s***m also began to suffer subtle changes in shape, a sign that the s***m were going stale. But the s***m of men with normal s***m counts showed little change in mobility after abstinence, and did not begin to go stale until much later." Continued at http://www.babyhopes.com/articles/abstaining.html
TMI, but I sure hope this helps!!