day 24 of your cycle is still only 10 days post ovulation if you have a 14 day luteal phase. as much as home preg tests say they can show up as early as ffive days before your period is due, it's not often that they do

as a reproductive technician you'd know all about embryo's having to develop to a certain point before they implant - it can't happen before at LEAST 6 dpo, usually 8 - and can be as late as 12 DPO - and once implantation occurs, your body has to start producing HCG and then has to climb to high enough levels to register. Doctors and hospital HPT's are notorious for not being as sensitive as many other tests - and you normally wouldn't do a hospital HPT on first morning urine (most concentrated hcg), so it's highly likely that you may not have anything show up for several more days yet

FWIW - i had a blood test at 15DPO and the concentration of HCG in that sample would not have been enough to trigger a GP HPT - i'd had 3 days running of positives at home though. my levels were VERY low but climbed beautifully and i'm now only weeks off delivery of our first bubba. i know implantation for this bubba occurred late (10 dpo) as i felt it happen. so don't give up hope, and don't stress if you're getting negatives at the moment - it may just be too early.