The 2nd Guards Cavalry Corps map for July 24th, 1944, shows the unit in Lukow. The map for July 23rd shows the unit some distance away, around Suchowola and Swierze.

Documents of the 2nd Guards CC mention the city very briefly.

"The 17th Guards Cavalry Division concentrated 2 km east of Lukow on the night of July 24th, 1944 after a 70 km march. After reconnaissance of routed north-west of Lukow, it resumed a joint offensive with the 3rd Guards CD after the 11th Tank Corps along the Lukow-Siedlce railroad at 6:00 on July 25, 1944. By 10:00 on July 25th, it reached the Rowze-Maly Oknin line."

Later on in the document we see why.

"From nonstop bombing by the enemy, there are losses in personnel, horses, and vehicles. The city of Lukow was destroyed completely."

Edit: seems I was too hasty, I found much more on Lukow from the 11th Tank Corps.

"July 23rd ... With careful reconnaissance in force, the [20th Tank Brigade] jointly with elements of the [11th Tank Corps] attacked Lukow from the south and southeast. After fierce fighting, the corps entered the city at 21:00, reached the railroad station, northeast and northern outskirts, cut off the highway, and set up defenses.

During the night, the enemy performed counterattacks with infantry supported by artillery in an attempt to knock the 20th TBr out of Lukow. The counterattacks were defeated.

July 24th

At dawn, when the rest of the corps arrived (less 65th TBr), efforts to clear out Lukow were renewed.

The enemy used stone buildings in Lukow to defend in individual strongholds.

After regrouping, elements of the corps swept the enemy out of Lukow in a rapid assault. By 18:00, the city was completely cleared of remaining submachinegunners.

Warehouses with ammunition, supplies, fuel, were captured two trains, six trucks, and two Ferdinand self propelled guns were destroyed.

With the goal of stopping the offensive, the enemy applied bomber and fighter aircraft in sorties of 25-90 aircraft simultaneously from the morning of July 24th to the night of July 25th without rest. Air strikes caused significant losses to attacking tanks. In order to conserve the unit's materiel, the tanks had to spread out. The command efforts became more complicated and the rate of the offensive was decreased."

Seems like the delay wasn't that great, since on July 25th the 11th TC was moving on towards Siedlce as mentioned above in the 2nd Guards CC journal.