If you are estimating drive time, I think Houston to Laredo in 5 hours is optimistic. You pick up 35 at mile marker 154 in SA so unless you are hammering non stop it will be closer to 6 hours. Maybe 5.5 but I prefer round up and be happy I'm "making good time" than round down and feel stressed over being "behind".
From Monterrey you'll take the periferico to MX40 through the Saltillo canyon. Actually there is a new cuota that replaces MX40 but roughly parallels it.
Now you have a choice. You can pick up MX57 just short of Saltillo (Ramos Arizpe) and take it down past Matehuala to San Luis Potosi. From there you take MX80 west to Ojuelos then southwest to Lagos. That would be my preference.
Or you can continue MX40/cuota to Saltillo, take MX54 to Zacatecas, then MX45 to Aquas Caliente and on to Lagos. I haven't been this route but hear the roads are good now.
Pick up a
Guia Roji to take with you, in the meantime use this
online map.
My time estimate would be:
Houston - Laredo, 6 hours
Border delays, 15 min. to 2 hours, I usually budget an hour
Monterrey MX85 - Ramos Arizpe (Saltillo) MX57, 1 hour
Saltillo MX57 - Matehuala MX57, 3 hours
Matehuala MX57 - San Luis MX57, 2 hours
San Luis MX57 - Lagos de Morena MX80, 2 hours
Total time: 17 hours (should cover petro stops and quick eats)