Once you are shopping steadily, you do not even notice the lag.
I learned pretty quickly to only shop out of shop funds. In the beginning, if I was running low on shop money and had a few shops coming up which required outlay, I did a few shops with quick paying companies in order to raise those funds.
Now, I've built up a shop fund of $2000, by adding some of my shop fees to the shop account some time ago, over time. Things like cell phone shops, a dealership here or there, banks, etc. Now, reimbursements go back into that fund, and I keep the shop fee.
I keep a shop fund of $2000 because sometimes I do a glut of high-outlay shops, like carpet cleaning, designer clothing/bags, etc. Realistically, though, in a normal month-to-month, I only spend about $700 out of that and get reimbursed some time later. With some of my infrequent, high-outlay shop companies taking 2-3 months to pay, having that $2000 set aside really comes in handy.
Some of the faster-paying companies are
-GfK (10-14 days)
Bestmark (21 days)
CORI (7-14 days)
DJC (7-21 days, sometimes as quick as 2-3 days)
Maritz (Twice monthly)
The Brandt Group (7-14 days) [And John is really, really awesome about processing them earlier if you need it]
Marketforce (10th of the following month) [ Do a glut of shops right in the last week of the month in order to see it within two weeks!]
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Plan the work. Work the plan.